It has been a maxim of statutory construction since [1804] that an act of congress ought never to be construed to violate the law of nations, if any other possible construction remains. While RFRA plainly applies to Federal law, the statute at no point clearly evidences an intention to abrogate or modify treaty obligations. Because treaty rights and obligations are too fundamental to be easily cast aside courts should be most cautious before interpreting RFRA in such manner as to violate international agreements. [cites removed]
So said Solicitor General Paul D. Clement is a brief against a claim brought by a religious group to import a certain drug to use as part of their religious ceremonies. RFRA (Religious Freedom Restoration Act) as applied to the states was declared unconstitutional by the Supreme Court, Justices O'Connor, Souter, and Breyer dissenting. A pretty narrow application respecting the federal government will be decided this term, perhaps on narrow statutory grounds.
So, apparently, the "law of nations" (international law) should be given special respect when the U.S. Congress acts, the President carries forth laws that they enact, and when the Supreme Court interprets them. "Any other possible construction" is pretty broad, not "reasonable" or even "probably accurate." Of course, if the Constitution compelled otherwise, it would not be "possible."
Anyway, it is nice that the administration is so very concerned with international law and treaty obligations.