New York City Mayor Bill de Blasio blasted the National Football League’s decision to penalize players for kneeling during the national anthem.

“Un-American. Just plain un-American,” de Blasio declared on MSNBC’s Morning Joe. “It doesn’t make sense. You know, we would not tolerate it if any other employer said that their employees cannot express their beliefs,” he said. “You know, right away you’d say violation of the First Amendment.”

“I don’t understand why the owners think they can get away from this in any way, shape or form,” de Blasio said. “But what they’re doing ultimately is simply bringing more attention to the cause of players, who are saying there’s an injustice that has to be addressed.” He was not alone in his reaction.

But the NFL is adamant that “today’s decision will keep our focus on the game and the extraordinary athletes who play it — and on our fans who enjoy it,” according to NFL Commissioner Roger Goodell. The new rule will fine any player who kneels during the singing of the national anthem before the start of a game.

President Donald Trump has praised the decision — and he had strong words for those who enacted the protest. “I don’t think people should be staying in locker rooms, but still I think it’s good,” he said. “You have to stand proudly for the national anthem or you shouldn’t be playing, maybe you shouldn’t be in the country.”