The Department of Homeland Security is broadening federal immigration authorities’ ability to detain legal refugees who have not yet obtained green cards, citing national security concerns and the need to ensure refugees undergo additional screening, according to a DHS memo obtained by CNN.

Immigration officers may “arrest and detain” refugees “who have failed to adjust” to lawful permanent resident status one year after being admitted to the US, according to the Wednesday memo, which was submitted by Justice Department attorneys as part of a federal court filing.

“When a refugee is admitted to the United States, the admission is conditional and subject to a mandatory review after one year,” the memo reads, noting refugees who are detained may remain in custody “for the duration of the inspection and examination process.”

The memo, issued by US Citizenship and Immigration Services Director Joseph Edlow and Acting US Immigration and Customs Enforcement Director Todd Lyons, rescinds previous government policy regarding refugees who have been in the country for one year.

Failure to obtain a green card after one year was not grounds for detention or removal from the US under previous policy, and refugees who were arrested had to either be released within 48 hours or the DHS was required to initiate removal proceedings.

“Refugees may be considered to have voluntarily returned to custody” by submitting application paperwork and appearing at scheduled appointments with immigration services, according to the new memo.

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Previous department policy “created a population of conditional refugees who had not been fully re-screened, with associated public safety and national security risks,” the memo says, and the new “detain-and-inspect requirement ensures that refugees are re-vetted after one year.”

Refugee resettlement groups promptly decried the new policy.

“This memo was done in secret, with zero coordination with the organizations that serve refugees,” said Beth Oppenheim, CEO of refugee agency HIAS. “This policy is a transparent effort to detain and potentially deport thousands of people who are legally present in this country, people the US government itself welcomed after years of extreme vetting,” she added.