“Many have hypothesized that China might demand ByteDance, TikTok’s parent company, turn over Americans’ data or use TikTok to push disinformation in some way, but neither Montana nor the U.S. government have pointed to any evidence that China is actually doing this,” Ms. Krishnan said. “That’s a problem because speculative harms can’t justify a total ban on a communications platform, particularly one that’s used by hundreds of thousands of Montanans daily.”

In addition to the potential legal fight, many experts raised questions about whether the law could realistically be enforced. Internet users can utilize virtual private network software to disguise their location. Individuals who live in Montana border towns could have access to TikTok and other mobile apps through cellular towers in neighboring states.

In an email, Emilee Cantrell, a spokeswoman for the state’s attorney general, said there was existing technology for restricting app usage within a specific location. The technique, known as geofencing, is “already in use across the gaming industry,” which the state’s Justice Department also regulates, Ms. Cantrell said.

“A basic internet search will show you companies that provide geolocation compliance,” she said. If companies do not comply with the ban, she continued, the agency “will investigate and hold offending entities accountable in accordance with the law.”

The legislation puts the onus for enforcing the ban on TikTok, Apple and Google. Under the law, TikTok could be fined $10,000 for each individual violation of the ban and face an additional $10,000 fine every day a violation continues. Apple and Google would face the same fines if they allowed the app to be downloaded in the state.