There are media reports that the U.S. Chamber of Commerce is considering a lawsuit challenging the President's proposed tariffs against Mexico. I hope they do so. They have a good chance of winning. In this case, the Administration has no clothes.
The International Emergency Economic Powers Act (IEEPA), which is the statutory authority cited by the President, grants two types of authority. One gives the President the power to freeze the assets of foreign nationals and/or foreign governments. The other gives the President the power to suspend commerce (or types of commerce) with another nation. Nothing in the Act suggests that the President is given the power to levy tariffs on another nation. Indeed, there are many reasons to doubt that such a power exists.
First, Congress has delegated tariff authority in other statutes that do not apply here. For instance, the President can (and has) imposed tariffs on China in response to unfair trade practices based on clear statutory authority. The lack of such an express delegation in the IEEPA implies no tariff authority.
Second, there appears to be no precedent for a President using the IEEPA to impose tariffs. (I say appears because I cannot find an example. If there is one, then I would like to know.)
Third, there is no indication from the legislative history of the IEEPA that Congress intended to give the President the authority to raise tariffs.
Fourth, there is no judicial authority for the President's proposed tariffs. Moreover, the Supreme Court's careful analysis of the IEEPA in Dames & Moore v. Regan is considerably narrower than the President's view.
The argument in favor of the proposed Mexican tariffs is basically a crude kind of a fortiori logic. Because the President can ban commerce from Mexico under the IEEPA, he must be able to impose the lesser sanction of tariffs. The conclusion does not follow from the premise. The greater does not always imply the lesser, as Congress is not bound to delegate its authority that way. Indeed, Congress might well guard its taxing authority far more jealously because that authority is easier to exercise as compared to a commercial ban.
In conclusion, the proposed Mexican tariffs are illegal. Interested parties should prepare to file suit.