President Donald Trump declared that people protesting federal immigration enforcement actions in Paramount this weekend were breaking the law by wearing masks and would be arrested for doing so.

“Great job by the National Guard in Los Angeles after two days of violence, clashes and unrest. These Radical Left protests, by instigators and often paid troublemakers, will NOT BE TOLERATED,” he wrote in a post on his Truth Social network late Saturday night, ahead of the National Guard’s arrival in the city on Sunday morning. “Also, from now on, MASKS WILL NOT BE ALLOWED to be worn at protests.”

The prohibition won’t stand up in court, according to Jonathan Markovitz, a staff attorney with the American Civil Liberties Union of Southern California.

“Trump’s threat to arrest anyone wearing masks at protests is blatantly unconstitutional,” he wrote in an email Monday. “The Supreme Court has recognized that there are times where anonymity is essential to allow people to exercise their constitutional rights.”

The protesters in Paramount and elsewhere opposing the administration’s immigration enforcement actions have reason to conceal their identities, Markovitz wrote.

“In the current political climate, people who seek to challenge policies or practices that harm vulnerable or dispossessed communities have been especially likely to be targeted for violent reprisal,” he wrote. “It is understandable that they would take measures to avoid such reprisal, as well as to avoid potentially blatant political prosecution. Trump has no authority to carry out his threat, but his attempt to chill free speech is reprehensible.”

But there’s no absolute right to wear a mask in public under all circumstances.

California has an 1872 law that bans wearing a mask, “false whiskers,” or other personal disguises for the purpose of concealing their identity in connection with breaking the law. Those who violate it are guilty of a misdemeanor.

A Southern California legislator condemned Trump’s mask declaration on Monday.

“Prohibiting masks at protests are ridiculous,” Assemblymember Mark González, D-Los Angeles, said Monday afternoon. “Protesters have the right to face coverings. It’s a violation of basic rights.”

But González said he witnessed firsthand masked troublemakers showing up during the aftermath of a protest Friday in Chinatown.

“Agitators showed up, full masks, goggles, sunglasses, you name it,” González said. “And they immediately started jumping on vehicles.”

He said he believes the masked protesters — armed with sledgehammers and vandalizing local neighborhoods while carrying Mexican flags — were there to help create a climate of chaos.

“I don’t have proof that these are Trump supporters, but this is what Trump wants,” González said.

Trump is opposed to mask-wearing protesters, asking “what do these people have to hide, and why???” in his post. But masked Immigration and Customs Enforcement agents have been at the heart of many immigration raids in recent weeks.

On Friday, House Speaker Mike Johnson, R-La., told Fox News that Immigration and Customs Enforcement agents need to be masked and anonymous for their own protection.

“They need to back off of ICE and respect our agents and stop protesting against them,” he said. “They’re trying to uphold the rule of law, and they don’t want to be targeted by Democrat activists. So I’m in favor of whatever protocol.”

Since returning to office, Trump has conducted an unprecedented immigration enforcement campaign. The White House has said it intends to deport 1 million people a year. According to the administration, between Trump’s inauguration on Jan. 20 and April 1, more than 100,000 undocumented immigrants were deported from the U.S.