The controversial H-1B visa has been highlighted in a new report on research that found 55 percent of U.S. tech startups valued at $1 billion or more were founded or co-founded by immigrants.

Among the foreign entrepreneurs who used the H-1B visa to get established in the U.S. are SpaceX CEO Elon Musk, who’s also CEO of Tesla; Michelle Zatlyn, chief operating officer of San Francisco network-services firm Cloudflare; and Jyoti Bansal, founder of AppDynamics, a San Francisco performance management and operations analytics company, according to the report from the National Foundation for American Policy.

The H-1B has become a target for the administration of President Donald Trump, which has reportedly increased rejections and scrutiny of applications for the visa, and plans to change the H-1B’s lottery-based award system to favor more highly skilled workers. Silicon Valley tech firms rely heavily on the H-1B, and have lobbied hard for an increase to the annual 85,000 cap on new visas. Critics point to reported abuses, and allege that companies use the H-1B to supplant American workers with cheaper foreign labor.

Musk, born in South Africa, received an H-1B after earning multiple degrees from the University of Pennsylvania, the report said. Cloudflare co-founder Zatlyn, a Canadian, was at first denied an H-1B, but ultimately got one. “If I hadn’t obtained the visa I would have gone back to Canada and tried to work on Cloudflare from there,” she told the foundation.

“If that had happened, Cloudflare would not be where it is today.”

Bansal of AppDynamics — bought by Cisco last year for $3.7 billion — received an H-1B in 2000, but had to wait seven years for a green card, watching some friends in similar situations get frustrated and leave the U.S., according to the report.

The research found that of 91 “unicorn” startups in the U.S. valued at $1 billion or more, 50 were founded or co-founded by immigrants, the report said.

Other unicorns created or co-created by immigrants include San Francisco-based Uber, co-founded by Canadian Garrett Camp; New York’s WeWork, co-founded by Israeli-American Adam Neumann; and Palantir of Palo Alto, co-founded by Peter Thiel, who was born in Germany, according to the report.