LOS ANGELES, United States, May 13, 2025 (AFP) - Hollywood studios and unions representing movie workers joined forces Monday to urge US President Donald Trump to give tax breaks to US-made films.

The joint letter, which was also signed by Jon Voight and Sylvester Stallone -- two of Trump's "ambassadors" to Hollywood -- comes days after the Republican president said he wanted to impose 100 percent tariffs on foreign films in a bid to help the domestic industry.

The letter thanks Trump "for the support you have shown our industry," and for drawing attention to production fleeing overseas.

But it makes no mention of Trump's tariff plan, a proposal that was met with bafflement across the industry, with observers saying they had no idea how such a tax might work.

"Currently, more than 80 countries offer production tax incentives and as a result, numerous productions that could have been shot in America have instead located elsewhere," says the letter.

"Returning more production to the United States will require a national approach and broad-based policy solutions, including... longer term initiatives such as implementing a federal film and television tax incentive."

The idea of a federal tax credit scheme was also suggested last week by California Governor Gavin Newsom.

The letter, from the Motion Picture Association -- an umbrella grouping for major studios and streamers -- and unions representing directors, actors and writers, suggests a number of tax deductions that would make movie-making cheaper.

"A domestic production incentive would make the US market more competitive and able to retain and return high-paying jobs tied to film and television productions -- and the use of this deduction has historically promoted significant economic and job growth," it says.

America's movie industry has gradually moved away from its traditional home in and around Hollywood as production has shifted to cheaper locations.

The number of shooting days in Los Angeles reached an all-time low last year -- lower even than during the Covid-19 pandemic, when filming shut down completely.

Fewer than one in five film or TV series broadcast in the United States was produced in California, according to FilmLA, an organization that tracks the movie industry.

The loss of that production has a significant economic impact.

According to the letter to Trump, each day a film shoots on location it spends more than $670,000, and employs nearly 1,500 people.

On May 4, Trump declared on social media that "the Movie Industry in America is DYING a very fast death."

He said he had told the Department of Commerce and the Office of the US Trade Representative to levy a 100 percent tariff "on any and all Movies coming into our Country that are produced in Foreign Lands."