The western US state of Montana on Thursday was on the verge of implementing a total ban on TikTok, after a proposal passed a key hurdle in its legislature.

If enacted, the proposed law would be unprecedented and test the legal waters for a national ban of the popular Chinese-owned app, a fate that is increasingly being called for in Washington.

Montana's Republican-dominated lower house overwhelmingly voted for a complete ban, with a final vote set for Friday before it goes to the state's governor to become law.

It passed by 60 votes for and 39 against.

TikTok said US courts would likely have the final word.

"The bill's champions have admitted that they have no feasible plan for operationalizing this attempt to censor American voices and that the bill's constitutionality will be decided by the courts," TikTok spokeswoman Brooke Oberwetter said in response to an AFP inquiry.

"We will continue to fight for TikTok users and creators in Montana whose livelihoods and First Amendment rights are threatened by this egregious government overreach."

TikTok, despite its immense popularity, is caught in a battle of wills with US government and politicians, and now faces an ultimatum by the White House that it split from its Chinese owners or stop operating in America.

"We are facing a threat unlike any other from the Chinese Communist Party hiding behind TikTok where they can spy on Americans by collecting personal information by keystrokes and even user locations," said Representative Brandon Ler, defending the Montana bill.

Under the proposed law, Apple and Google would have to remove TikTok from their app stores and companies will face daily fines of $10,000 if found in violation.

The proposed ban would take effect in 2024, but faces almost certain legal challenges, given its unprecedented nature in the United States, possibly going all the way to the Supreme Court in Washington.

"I think there are a lot of ramifications, not the least of which is how you would do it," said University of Richmond law professor Carl Tobias.

"It is hard to see how the state would be able to defend it and win," Tobias told AFP.

When an earlier version of the bill passed in the Montana senate, TikTok decried a "disastrous precedent" that would be an "egregious violation" of free speech in the state.

'Don't have to care'

Free speech advocates also opposed the legislation.

"Passing this legislation would flout the First Amendment and would trample on Montanans' constitutional right to freedom of speech," said a letter to Montana lawmakers from the ACLU and other associations.

Montana's turn of the screws on TikTok comes as the app faces several hard-hitting, but legally tenuous, proposals of national legislation -- including one bill backed by the White House that could pave the way for a ban of the app.

"Part of the problem is that politicians don't have to care about what happens after they've passed the law," said Ari Cohn, free speech counsel at TechFreedom, a think tank.

"They're all too happy to consider legislation that will get easily struck down by the courts. It's just the nature of politics, unfortunately," he told AFP.

© Agence France-Presse