President-elect Donald Trump on Tuesday suggested that people who burn the American flag should lose their citizenship.

This goes against current U.S. law, as well as a landmark Supreme Court case.

Nobody should be allowed to burn the American flag - if they do, there must be consequences - perhaps loss of citizenship or year in jail! — Donald J. Trump (@realDonaldTrump) November 29, 2016

Burning the flag is completely legal in the U.S. As the Supreme Court ruled in 1989’s Texas v. Johnson, it’s protected as free speech under the First Amendment. The late Justice Antonin Scalia, who Trump often praises, joined the majority opinion in that case.

Lawmakers have in the past floated the idea of making the practice illegal, but none have gone as far as to suggest revoking citizenship. Citizenship is very difficult to take away; broadly speaking, an American would only lose his or her nationality by pledging allegiance to another country, committing treason, or voluntarily giving it up.

As author Anand Giridharadas points out, Trump’s comments call to mind the history of fascist regimes:

Let us take this seriously, because it may be something new: the explicit articulation that doing legal things could cost you citizenship. — Anand Giridharadas (@AnandWrites) November 29, 2016

Some history of denaturalization. Spoiler alert: these countries weren't headed in good directions. pic.twitter.com/X1E9fey3sQ — Anand Giridharadas (@AnandWrites) November 29, 2016

Trump has contradicted the U.S. Constitution before. He’s promised to crack down on the press (a possible violation of the First Amendment), vowed to ban Muslims from entering the country (which could go against the Equal Protection Clause), and suggested we should torture people because they deserve it (cruel and unusual punishment).

This article has been updated with information on denaturalization and Giridharadas’ tweets.