U.S. lawmakers want to force a sale of TikTok by its Chinese owner or ban it from app stores, which legal experts said would set up a showdown with the social media company over the U.S. Constitution's First Amendment free speech protections.

While the bill itself does not say anything about speech, the proposal has alarmed civil rights advocates, TikTok and users of the app, all of whom could sue to block the proposal if it becomes law.

Legal experts said opponents of the law could argue it infringes free speech by preventing users from expressing themselves and businesses from using the app to promote their products. TikTok has already beaten back a similar attempt to ban its use in the U.S. state of Montana, although the state is appealing that ruling.

Jameel Jaffer, executive director of the Knight First Amendment Institute called the measure "censorship — plain and simple" in a letter that his group and others sent this week to lawmakers.

A court that agrees with that assessment would apply strict scrutiny, meaning the government would have to prove it has not violated speech rights. This hurdle would make it more likely for the law to be blocked.

The bill's promoters have argued it has nothing to do with speech but merely regulates a commercial activity by requiring TikTok's Beijing-based owner ByteDance to sell the U.S. operations, denying China easy access to users' data.

The bill had strong bipartisan support in the U.S. House but still must clear the U.S. Senate, which could rework the proposal. U.S. President Joe Biden, whose re-election campaign uses TikTok, has said he supports the proposal.

If the bill becomes law, and users and TikTok sue to block enforcement, a key part of any legal challenge will be the court's view of the standard applied in reviewing the law.

Legal experts said if the government winds up fighting a First Amendment case under the strict scrutiny standard, it must prove national security or some other compelling government interest is at stake. It will also have to prove the law was "narrowly tailored" to address that particular issue.

Critics spot a weakness in the government's potential case on this point: Washington thus far has seemed unconcerned about abuse of users' data by other social media platforms.

Plenty of companies such as Meta Platform's Facebook collect, store and share users' data, but the government has never treated that activity as a national security threat or enacted data protections.

The Electronic Frontier Foundation's David Greene said that if the U.S. were really concerned about China and data privacy, it would push legislation that applies to all social media companies, not just TikTok.

The government would need to convince a court the measure is not a limitation on speech but a regulation of a commercial transaction and a way to protect national security.

The government would argue that TikTok could continue to operate and U.S. users continue to use it, just not under Chinese ownership, so the law's effect on speech was "incidental" and permitted.

In November, a U.S. federal judge in Montana blocked Montana’s effort to ban TikTok within the state. TikTok and some users filed a pair of First Amendment lawsuits challenging the proposed ban, which had been set to take effect in January.

U.S. District Judge Donald Molloy issued a preliminary injunction halting the state’s ban, saying it "violates the Constitution in more ways than one" and "oversteps state power." Montana, backed by Virginia and 18 other states, is challenging the order on appeal.

"The law is not narrowly tailored, nor does it leave open any alternative channels for targeted communication of information," Molloy wrote.

(Reporting by Mike Scarcella; Editing by Tom Hals and David Gregorio)