Apple and Google are warning some U.S-based employees on visas against traveling outside of the country to avoid the risk of getting stuck coming back, as the Trump administration toughens vetting of visa applicants, according to recent internal memos from the tech companies that were reviewed by NPR.

U.S. consulates and embassies have been reporting lengthy, sometimes months-long delays, for visa appointments following new rules from the Department of Homeland Security requiring travelers to undergo a screening of up to five years’ of their social media history — a move criticized by free speech advocates as a privacy invasion.

For Apple and Google, which together employ more than 300,000 employees and rely heavily on highly-skilled foreign workers, the increased vetting and reports of extended delays were enough for the companies to tell some of their staff to stay in the U.S. if they are able to avoid foreign travel.

“We recommend avoiding international travel at this time as you risk an extended stay outside of the U.S.,” Berry Appleman & Leiden, a law firm that works with Google, wrote to employees.

The law firm Fragomen, which works with Apple, wrote a similar message: “Given the recent updates and the possibility of unpredictable, extended delays when returning to the U.S., we strongly recommend that employees without a valid H-1B visa stamp avoid international travel for now,” the memo read. “If travel cannot be postponed, employees should connect with Apple Immigration and Fragomen in advance to discuss the risks.”

Apple and Google declined to comment on the advisories, which were first reported by Business Insider.

It’s the latest sign of how the Trump administration’s aggressive immigration policies are affecting the foreign-born workforce in the U.S.

Earlier this year, the White House announced that companies will be subjected to a $100,000 fee for all new H-1B visas, a type of visa popular among tech companies eager to hire highly skilled workers from abroad.

H-1Bs typically last three years, and applicants have to return to an embassy or consulate in their home country for a renewal, but reports suggest such a routine trip could lead to people being stranded for months as a result of the Trump administration’s new policies.

On Friday, The Washington Post reported that hundreds of visa holders who traveled to India to renew their H-1Bs had their appointments postponed with the State Department explaining that officials needed more time to ensure that no applicants “pose a threat to U.S. national security or public safety.”

At Google, the Alphabet Workers’ Union has been campaigning for additional protections for workers on H-1B visas. Those workers would be particularly vulnerable in the event Google carried out layoffs, since losing employer sponsorship could jeopardize their legal status, said Google software engineer Parul Koul, who leads the union.

The need to support H-1B holders at Google, she said, has “only become more urgent with all the scrutiny and heightened vetting by the Trump administration around the H1B program, and how the administration is coming for all other types of immigrant workers.”