President Trump is renewing his threat to impose a 100 percent tariff on foreign-made movies entering America, leaving major studios with more questions than answers about how their increasingly globe-spanning operations are likely to be affected.

Investors also appeared uncertain about the implications, nudging the stock prices of some studios up on the news while pushing others down. Among the most affected was Warner Brothers Discovery, down 1.72 percent at midday Monday.

“Our movie making business has been stolen from the United States of America, by other Countries, just like stealing ‘candy from a baby.’ California, with its weak and incompetent Governor, has been particularly hard hit!” Mr. Trump posted on his Truth Social account shortly before markets opened Monday.

“Therefore, in order to solve this long time, never ending problem, I will be imposing a 100% Tariff on any and all movies that are made outside of the United States. Thank you for your attention to this matter.”

The posting left a number of questions, including whether the tariff would be calculated based on production costs, box office sales, or some other formula; how it would be applied to joint productions between American and overseas studios, and whether it would apply only to theater releases or also to streaming offerings. Those details will affect not only studio profits but also ticket prices paid by movie-goers.

It was also not stated under what authority the tariffs would be applied. Some of Mr. Trump’s tariffs are already at risk of being struck down by the Supreme Court, which is to hear a challenge next month, though others have been found to be within his powers to apply without congressional action.

Mr. Trump first floated the idea of a 100 percent tariff on movies in May, prompting some consternation within the industry. Studio executives told Reuters at that time they were “flummoxed” by the logistical issues involved, given that the production and financing of modern films is often spread across multiple countries.

Canada, Britain, and Australia, for example, all offer tax incentives that have incentivized studios to shoot films on their territories, often involving American actors and personnel.

It is “cheaper for Hollywood studios to pay for everyone to get on planes, pay for hotels, because the cost of labor, lack of rebates and the ability to make things overseas is infinitely cheaper,” the vice chairman of United Talent Agency, Jay Sures, acknowledged to CNN in May.

Another unidentified industry insider told the network at the time that the tariff proposal “would represent a virtually complete halt of production.” The insider also argued that the plan was illegal and “too complex to enforce.”

In a rare tip toward bipartisanship, Senator Adam Schiff said he would be happy to work with the Trump administration to make Hollywood competitive again.

“I strongly support bringing movie making back to California and the U.S. Congress should pass a bipartisan globally-competitive federal film incentive to bring back production and jobs, rather than levy a tariff that could have unintended and damaging consequences. We have an opportunity to pass a major federal film tax credit. I’m ready to work with this administration and my colleagues on both sides of the aisle to get it done,” Mr. Schiff posted on X.

Reuters reported it has reached out to several major studios for reaction to Mr. Trump’s latest post but had not received any immediate response.