The training program, which was created in 1992 and extended the amount of time STEM graduates can participate in 2016, is popular with both international students and the U.S. universities that compete to enroll them. Though the H-1B visa is better known, there are many more F-1 visa recipients—nearly 400,000 last year. (Unlike the H-1B, the F-1 does not have a strict cap.) Under the Trump administration, though, the program increasingly appears under threat.

Recent administrations have described an ongoing shortage of STEM graduates as an urgent problem; the Bureau of Labor Statistics estimates that there will be 1 million job openings in computer occupations—the field expected to dominate STEM growth—from 2014 to 2024. But even though a growing number of students in the U.S. are earning bachelor’s degrees in computer science, they can’t keep pace with the number of available jobs.

The F-1 program has provided one avenue to do so. In the past, graduates participating in optional practical training could work in the U.S. for only one year. In 2008, though, the George W. Bush administration extended the amount of time international students in STEM optional practical training could stay, from 12 months to 29 months. In 2016, the Obama administration extended the window further, to 36 months. As a result, the number of international students in STEM fields approved to work in the U.S. after graduation jumped from about 34,000 in 2008 to 172,000 in 2016, according to the Pew Research Center, in an analysis of 1.5 million college graduates who participated in the optional practical training program between 2004 and 2016. Despite concerns about fake universities and visa fraud, the Pew research shows that the vast majority of graduates in the optional practical training program attend public universities or private, nonprofit colleges, not for-profit schools.

The immigrants fueling the gig economy

Last year, President Donald Trump directed Betsy DeVos, the secretary of education, to make promoting high-quality STEM and computer-science education a top priority. But when it comes to developing a STEM workforce, Trump has been most intent on training Americans, in particular. In July, he signed an executive order establishing a National Council for the American Worker, focused on “the skills crisis and the importance of STEM education.” The order quotes Trump as saying, quite explicitly, “We want to make sure that we have the workforce development programs we need to ensure these jobs are being filled by American workers.”

Partly because of stricter immigration policies but perhaps also because of Trump’s rhetoric, the number of F-1 visas is down 17 percent from 2016, and well below the recent peak of nearly 645,000 visas in 2015. The U.S. government does not disclose how many applications it receives or how many it rejects. In August, chief executives of companies such as Apple, JPMorgan Chase & Co., and Pepsico sent a letter to D.H.S., saying that making it harder for high-skilled workers to stay in the U.S. will hurt the economy.