TikTok, which says it has 7,000 employees in the United States, has been fighting back in the state for months.
It has run ads featuring Montana small businesses that use TikTok and given prewritten emails to users so they could contact Mr. Gianforte about opposing the bill.
The legislation prohibits mobile app stores, like those run by Apple and Google, from offering TikTok within the state.
A trade group funded by Apple and Google has said in recent months that it is impossible for the companies to prevent access to TikTok in a single state.
The battle in Montana erupted during a period of intense national scrutiny on TikTok, which boasts more than 150 million U.S. users.