A large controversial work-permit program for foreign students and recent graduates poses a high risk of foreign spying and trade-secrets theft and is vulnerable to fraud, according to a new report by the ombudsman for the U.S. immigration agency.

The Optional Practical Training program gives students and graduates up to three years to work in the U.S., and according to Pew Research is often used as a bridge between student visas and the H-1B visa intended for jobs requiring specialized skills. Silicon Valley’s technology giants rely heavily on OPT and the H-1B.

“There appears to be a high risk that the OPT is being used as a means for strategic adversaries to conduct espionage and technology transfer from the United States,” says the 2020 report to Congress from the Office of the Citizenship and Immigration Services Ombudsman. The report’s espionage warnings focused on risk from China, saying the OPT program’s vulnerability to spying and trade secret theft “has been largely ignored,” while citing a host of government and media reports addressing that issue since 2018.

Sarah Pierce, an analyst at the non-partisan Migration Policy Institute, called the focus on espionage “very out of left field and really surprising.” Concerns about spying in U.S. higher education would be more appropriately raised with regard to foreign-student visas, which are overseen by Immigration and Customs Enforcement, a separate agency, Pierce said.

Although the Ombudsman’s office describes itself as independent, it is within the U.S. Department of Homeland Security and reports directly to that agency’s chief. The office’s leadership is aligned with the immigration priorities of the administration of President Donald Trump, Pierce said, “which clearly brings into question the independence of the office.” However, Pierce said, “There are a lot of very legitimate labor concerns about the OPT.”

Citing media and government reports, the report also pointed to problems with OPT oversight and “significant indications that the OPT program is vulnerable to fraud” because it’s grown too large for the oversight dedicated to it.

An OPT permit essentially expands F-1 education visas for foreign college and university students so they can work while in school or after graduating. The program’s base-level permit lasts a year, but a “STEM extension” for people in science, technology, engineering and math allows participants to spend an additional two years working in the U.S. Major Bay Area tech companies were in 2018 among the top employers of OPT students on a STEM extension, according to Immigration and Customs Enforcement. Intel had 1,111; Google had 996; Facebook had 528; Apple had 433; Cisco had 322; and Oracle had 256, the agency reported.

About 200,162 OPT holders were employed in the U.S. in 2018, more than one-fifth of all foreign students, the Ombudsman’s report said. About a third of foreign students that year came from China, with India next at about a fifth. The OPT program grew 400% between 2008 and 2018, Pew Research has reported.

Emphasis in the report on how Chinese spies may be exploiting the OPT program echoes concerns raised by a group of Republican U.S. senators who have called for its suspension, and comments from Chad Wolfe, acting secretary of the U.S. Department of Homeland Security, during an April radio show. The report also cited the case of Weiyun “Kelly” Huang, a Chinese citizen sentenced in June to three years in prison after pleading guilty in federal court to conspiring to provide fake OPT certification to 2,685 foreign students. Central to her scheme was a Mountain View address, authorities alleged. Her indictment claimed one of her clients was a spy for the Chinese government.

President Donald Trump in an April executive order tasked officials with reviewing OPT and other non-immigrant permits and visas, but after the review took no action against OPT. Last year, Arizona Republican Congressman Paul Gosar, supported by immigration hardliners including Florida Rep. Matt Gaetz and Texas Rep. Louie Gohmert, introduced a “Fairness for High-Skilled Americans” bill — which has not progressed — to kill the OPT program. And a group of tech workers has been seeking an order banning the program since filing suit in 2014, arguing that OPT participants compete against U.S. workers for jobs.

Both OPT and the H-1B programs have become embroiled in America’s debate over immigration, with supporters, including major tech-industry employers, arguing the programs are crucial for securing the world’s top talent, and critics claiming they’re used to drive down wages and supplant U.S. workers.

The Ombudsman’s report also notes that the OPT program lacks many customary job protections for U.S. workers, and that the tech workers’ suit alleges that “employers are attracted to hiring OPT students by tax incentives aligned to the status of the students.” According to analyst Pierce, “It’s very possible that employers use the OPT program to hire foreign nationals at a discount.”