The ban of the Chinese-owned media giant is due to take effect on January 1, after Montana Governor Greg Gianforte signed the ban into law.
However, TikTok has already hit back at the move, arguing that it "infringes on the First Amendment rights of the people of Montana".
The tech company has also pointed out that it was used by "hundreds of thousands of people" in the state of Montana.
In a statement, the company added: "We want to reassure Montanans that they can continue using TikTok to express themselves, earn a living, and find community as we continue working to defend the rights of our users inside and outside of Montana."
The ban has also been criticised by Carl Szabo, who serves as the vice-president and general counsel of NetChoice, a trade group that counts Google and TikTok among its members.
Szabo described the decision in Montana as unconstitutional.
He said in a statement: "This is a clear violation of the constitution, which prohibits the government from blocking Americans from accessing constitutionally protected speech online via websites or apps."