Fake accounts violate Facebook’s rules, and even the Department of Homeland Security can’t create them, the social network told the Associated Press today in response to a new policy implemented by the agency.

In one of a series of changes to immigration policy last week, the department said employees at US Citizenship and Immigration Services, a division of DHS, could create fictitious accounts on social media to investigate the social media presence of an applicant for citizenship or a visa. This year, the Trump administration also started requiring applicants to list social media accounts as part of the visa screening process, a move that critics saw as an unnecessarily invasive measure.

Twitter is reviewing the policy

But the latest policy change could face a hurdle beyond civil liberties concerns: Facebook and Twitter have rules in place against fake personas.

“Law enforcement authorities, like everyone else, are required to use their real names on Facebook and we make this policy clear,” a Facebook spokesperson told the AP, which first noted the policy change last week. “Operating fake accounts is not allowed, and we will act on any violating accounts.” Twitter told the AP last week that using a fake persona violated their rules, but that the company was reviewing the policy.

“Incorporating reviews of publically available information on social media platforms in our threat detection work is a common sense measure to strengthen our vetting procedures and vigilance in safeguarding our legal immigration system from those [who] would seek to exploit and abuse it,” a USCIS spokesperson said in a statement. Under the policy, investigators are bound to use the accounts to view posted information, but not actively follow or interact with a user to obtain the information.

The policy comes as social media companies continue to face covert propaganda action on their platforms. Beyond attempts by Russia to influence the 2016 US presidential election, more recent efforts have also been unearthed. Last month, both Facebook and Twitter removed accounts believed to be linked to the Chinese government that spread propaganda about protests in Hong Kong.