[p. 62] Mr. Justice McKenna delivered the opinion of the court:

 This case involves the consideration of the validity under the Constitution of the United States of the imposition of double damages under an act of the state of Minnesota for a 'casual and involuntary trespass,' made by cutting or assisting to cut timber upon the lands of the state. The act is set out in the margin. [n. *]

 The action was brought to recover the sum of $51,324.42 for timber cut by plaintiffs in error from certain lands of [p. 63] the state 'without a valid and existing permit.' The question in the case revolves around this permit and the extensions of it alleged by plaintiffs in error to have been given.

 The findings of the court show the following facts: The state sold at public auction, in accordance with the statute, the timber on the lands to John F. Irwin, one of the plaintiffs in error, acting for himself and as agent of the Shevlin-Carpenter Company, and a permit was issued by the auditor and land commissioners of the state, which contained the following clause: 'That no extension of time of this permit shall be granted except as provided in § 24, chapter 163, General Laws 1895.' The section provides that no permit shall be issued to cover more than two seasons, and no permit shall be extended except by unanimous consent of the board of timber commissioners, and under no circumstances shall an extension be granted for more than one year, and then only for good and sufficient reasons. Irwin gave bond as required by law. On the 7th of May, 1902, the permit was extended until the 1st of June, 1903. At the time the permit was extended, the sum of $1,307, as required by law, was paid by plaintiffs in error into the treasury of the state, that sum being 25 per cent of the appraised value of the timber. In the winter of the years 1903-'4, plaintiffs in error, knowing that there had been one extension of the permit, and that that extension had expired, entered upon the land and cut and removed therefrom 2,444,020 feet of timber, which it was agreed was worth $6 per thousand feet, board measure. After the timber was cut, the surveyor general of the lumber district scaled and returned the amount of the same to the auditor of the state, which officer erroneously computed the amount due from the plaintiffs in error at the contract price of stumpage value thereof, as if the permit were still in force, finding the same to be $18,574.39. [p. 64] This amount was paid to the state, and no part of it has been returned.

 From these facts the court deduced the conclusion that the permit expired on the 1st of June, 1902, and that the extension thereof expired on the 1st of June, 1903, and that after the latter date it was of no effect and absolutely void, and was known to be so to plaintiffs in error when they cut the timber in controversy, and that their entry upon the lands was in violation of the law. They were adjudged wilful violators of the law, and damages were assessed against them at treble the value of the timber; to wit, $43,992.36. The court, however, decided that a deduction should be made from that sum of $16,997, money paid by plaintiffs in error to the state after the permit had expired. There were other sums of money, with the disposition of which we are not concerned. Judgment was entered against plaintiffs in error for the sum of $26,995.17. The supreme court affirmed the conclusion of the trial court, that the permit had expired, and that the cutting and removing of the timber were illegal, but disagreed with that court as to the character of the trespass. The supreme court said: 'The finding of the trial court that appellant was guilty of a wilful trespass is not sustained by the evidence. On the contrary, the record conclusively shows that appellant had reasonable ground for believing authority had been granted, and honestly acted on such belief.' [102 Minn. 479, 113 N. W. 638.] The court hence decided that the judgment should only have been for double, not treble, damages, saying: 'Being of opinion that in this action the state is limited to a recovery of double damages, and the judgment ber cut having been paid for, the judgment is necessarily to the value as found.' The case was remanded with directions to reduce the judgment to $14,664.12. In all other respects it was affirmed.

 On the question of the validity of the law under the 14th Amendment of the Constitution of the United [p. 65] States, the court said: 'On a former appeal upon demurrer to the complaint (99 Minn. 158, 108 N. W. 935, 9 A. & E. Ann. Cas. 634), the constitutional questions were raised, and it was there held that the act was constitutional, and that in case of trespass the state might recover either the double value of the property taken, or treble its value, according to whether the facts constituted a casual or involuntary, or a wilful and unlawful trespass. We adhere to that decision, and for the reasons set forth in the opinion then filed.'

 This statement of the facts and the rulings of the courts of Minnesota exhibit the controversy, the state contending that the penalties of the statute are incurred by a casual or involuntary trespass; the plaintiffs in error insisting that to attach that consequence to acts done in good faith violates the due process clause of the 14th Amendment of the Constitution of the United States.

 Another contention is made by plaintiffs in error. The statute makes one who cuts or removes timber contrary to the provisions of the act, or 'without conforming in each and every respect thereto,' guilty of a felony, and prescribes a fine or imprisonment, or both, in case the trespass is adjudged to have been wilful. . . .

* * *

 The next contention of plaintiffs in error is that 'both the provisions of § 7 make a casual and involuntary trespasser liable to the state in double damages, and that declaring his act a felony violates the 14th Amendment,' because those provisions 'eliminate altogether the question of intent,' and that the 'elimination of intent as an element of an offense is contrary to the requirements of due process of law.' To support the contention, plaintiffs in error attack the power of a legislature to make an innocent act a crime, and say that the 'principle that the legislature cannot, by its mere flat, make an act otherwise innocent a crime, and punishable as such, is one to [p. 68] which this court will give effect, even though it be not expressly enunciated by the Constitution.' The principle as thus expressed is very general, and takes no account of whether a law have prospective or retrospective operation. It would seem, therefore, to destroy the well- recognized distinction between mala in se and mala prohibita. The principle contended for is probably not intended to be taken so broadly, and its generality is further limited by concession that it may have exceptions 'where so-called criminal negligence supplies a place of criminal intent, or where, in a few instances, the public welfare has made it necessary to declare a crime, irrespective of the actor's intent.' A concession of exceptions would seem to destroy the principle. If the principle gets its life or its protection from the 14th Amendment, it cannot be destroyed by the legislature upon any conception of the public welfare. The Constitution declares the principle upon which the public welfare is to be promoted, and opposing ones cannot be substituted. Connolly v. Union Sewer Pipe Co. 184 U. S. 540, 558, 46 L. ed. 679, 689, 22 Sup. Ct. Rep. 431.

 It will be seen that the foundation of the arguments of plaintiffs in error is that their trespass was an innocent act. There is some ambiguity as to what is meant by 'innocence.' They quote Mr. Justice Chase in Calder v. Bull, 3 Dall. 386, 1 L. ed. 648. It was there said that 'a law that punished a citizen for an innocent action, or, in other words, for an act which, when done, was in violation of no existing law,' could not 'be considered a righful exercise of legislative power.' But it was said: 'The legislature may enjoin, permit, forbid, and punish; they may declare new crimes and establish rules of conduct for all its citizens in future cases.' In other words, innocence cannot be asserted of an action which violates existing law, and ignorance of the law will not excuse. The law in controversy has no ex post facto element or effect in it. It was existing law when the trespass of plaintiffs in error [p. 69] was committed, and a trespass is a legal wrong, not an innocent act. There is no element of deception or surprise in the law. When the permit was issued, plaintiffs in error knew the limitations of it, and they took it at the risk and consequences of transgression. The state sought to guard against its wilful or accidental abuse. Permits had been abused and the lands of the state despoiled of their timber. The offenders were difficult to detect, or, if detected, the character of their acts, whether wilful, accidental, or involuntary, equally difficult to establish; and the state, the supreme court said, had been 'defrauded and robbed of large sums of money.' Double and treble damages and a criminal prosecution were provided to meet the situation. It would be strange, indeed, if it were not within the competency of the legislature. To hold otherwise would take from the legislature the power to adjust legislation to evils as they arise and to the ways by which they may be effected. . . .

 We do not understand the position of plaintiffs in error to be that a legislature may not prescribe a larger measure of damages than simple compensation, but that anything in excess of such compensation is punishment, and cannot be constitutionally prescribed where there is no 'conscious intent' to do wrong. And yet plaintiffs in error except from the principle 'certain instances within the police power,' overlooking that the principle, if it exist at all, must be universal. It is true that the police [p. 70] power of a state is the least limitable of its powers, but even it may not transcend the prohibition of the Constitution of the United States. If, as contended, intent is an essential element of crime, or, more restrictively, if intent is essential to the legality of penalties, it must be so, no matter under what power of the state they are prescribed. Plaintiffs in error, while considering there may be exceptions to the principle contended for in the exercise of the police power, urge that the legislation in controversy is not of that character. The supreme court of the state, however, expressed a different view. It decided that the legislation was in effect an exercise of the police power, and cited a number of cases to sustain the proposition that public policy may require that in the prohibition or punishment of particular acts it may be provided that he who shall do them shall do them at his peril, and will not be heard to plead in defense good faith or ignorance. Those cases are set forth in the opinion of the court, and some of them reviewed.

 We will not repeat them. It was recognized that such legislation may, in particular instances, be harsh, but we can only say again what we have so often said, that this court cannot set aside legislation because it is harsh.

* * *

 Judgment affirmed.

 Mr. Justice Harlan concurs in the result.
 

* Sec. 7. If any person, firm, or corporation, without a valid and existing permit therefor, cuts, or employs or induces any other person, firm, or corporation to cut or assist in cutting, any timber of whatsoever description, on state lands, or removes or carries away, or employs, or induces, or assists any other person, firm, or corporation to remove or carry away, any such timber or other property, he shall be liable to the state in treble damages, if such trespass is adjudged to have been wilful; but double damages only in case the trespass is adjudged to have been casual and involuntary, and shall have no right whatsoever to any remuneration or allowance for labor or expenses incurred in removing such other property, cutting such timber, preparing the same for market, or transporting the same to or towards market.
Whoever cuts or removes, or employs or induces any other person, firm, or corporation to cut or remove, any timber or other property from state  lands, contrary to the provisions of this act, or without conforming in each and every respect thereto, shall be guilty of a felony, and upon conviction thereof shall be punished by a fine not exceeding one thousand (1,000) dollars, or by imprisonment in the state prison not exceeding two (2) years, or by both, in case the trespass is adjudged to have been wilful.
Whenever any timber so cut is intermingled with any other timber, or whenever other property taken from state lands is intermingled with other property, the state may seize and sell the whole quantity so intermingled, pursuant to the provisions of section forty (40) of this act, and such other timber or property shall be presumed to have been also cut from state lands.
Providing the intermingling of timber above referred to shall only apply to cases having been adjudged as wilful trespass. [Gen. Laws 1895, chap. 163, p. 352.]