The Trump administration has enacted a pause on all immigration applications filed by migrants from Latin America and Ukraine allowed into the U.S. under certain Biden-era programs, citing fraud and security concerns, according to two U.S. officials and an internal memo obtained by CBS News.

The application freeze will remain in place indefinitely while government officials work to identify potential cases of fraud and enhance vetting procedures to mitigate concerns related to national security and public safety, according to the directive.

The move, which had not been previously reported, threatens to cast a cloud of uncertainty over many migrants who were in the process of applying for various immigration benefits that would allow them to stay in the U.S. legally and, in some cases, permanently.

While the exact number of affected migrants is unclear, the hold on applications applies to several Biden administration programs that allowed hundreds of thousands of foreigners to come to the U.S. legally through an immigration law known as parole. That law empowers the U.S. government to welcome foreigners quickly on humanitarian or public benefit grounds.