Five TikTok users are calling on a federal court to overturn Montana's ban on the video-sharing app, arguing that it violates their right to freedom of speech.
The lawsuit was filed hours after Montana Governor Greg Gianforte signed the unprecedented ban into law on Wednesday.
Mr Gianforte said on Twitter he endorsed the ban to “protect Montanans' personal and private data from the Chinese Communist Party”.
The state is trying to exercise national security power that only the federal government can wield and is violating free speech rights in the process, the suit argued.
“Montana can no more ban its residents from viewing or posting to TikTok than it could ban The Wall Street Journal because of who owns it or the ideas it publishes,” the lawsuit argued.
The app is owned by Chinese firm ByteDance and some US politicians have suggested it is under the tutelage of the Chinese government and is a tool of espionage for Beijing, which the company denies.
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Plaintiffs named in the suit included a former US Marine Corps sergeant, a mother living with her family on a ranch, a businesswoman who sells swimwear and a student who posts video snippets about her outdoor adventures.
The TikTok creators have significant followings and make money from the platform, the lawsuit claims.
It calls for the court to stop Montana enforcing the ban and to pay the legal costs of the plaintiffs.
Montana became the first US state to ban TikTok, with the law set to take effect next year as debate escalates over the popular video app's impact on security.
The prohibition will serve as a legal test for a national ban of the Chinese-owned platform, for which politicians in Washington are increasingly calling.
The ban makes it an offence each time “a user accesses TikTok, is offered the ability to access TikTok, or is offered the ability to download TikTok”.
Each offence is punishable by a $10,000 fine every day it takes place.
Under the law, Apple and Google will have to remove TikTok from their app stores and companies will potentially face daily fines.
The ban will take effect in 2024, but be voided if TikTok is acquired by a company incorporated in a country not designated by the US as a foreign adversary, the law reads.
The legislation is the latest skirmish between TikTok and western governments, with the app already banned on government devices in the US, Canada and several countries in Europe.