People who take part in Saturday’s mass “No Kings” protest against President Donald Trump’s administration may be targeted for federal government surveillance with a range of technology that could include facial recognition and phone hacking, civil libertarians said.

“No Kings” organizers expect 2,600 rallies across all 50 U.S. states. But the level of surveillance at protests and the type of technology in use is likely to be both location-specific and dependent on the police forces present, said Thorin Klosowski, a security and privacy activist with the Electronic Frontier Foundation, said Friday.

“Under previous administrations, law enforcement surveillance of peaceful demonstrations was already commonplace and corrosive of free expression,” Ryan Shapiro, executive director of government transparency group Property of the People, said in an email Friday.

“Given Trump’s open hostility to even minor dissent, such surveillance now poses an existential threat to what remains of American democracy and only underscores the need for mass protest.” One federal law enforcement agency, the Department of Homeland Security’s Immigration and Customs Enforcement, has been implementing Trump’s immigration crackdown and has amassed a digital surveillance arsenal, according to various news outlets.

Surveillance isn’t limited to federal agencies. Multiple local police departments have used facial recognition technology, with laws governing its use varying from state to state, news outlet Stateline reported in February. Nate Wessler, deputy director of the ACLU Speech, Privacy, and Technology Project, said that different technologies have different legal requirements and require specific court authorization for focused and limited use. But it’s not easy to prove that a specific person was included in an inappropriate collection of data, Wessler said.

“This is a recurring problem in trying to constrain government’s use of surveillance technologies,” he said in an interview. “They are often designed to work surreptitiously and it can be extremely hard to prove whether you or any particular person was swept up in this kind of surveillance.” The Trump administration "sidelined or fired Homeland Security staffers who might have curbed surveillance “excesses,” said Don Bell, policy counsel for the Constitution Project at the Project on Government Oversight.

Although the first “No Kings” protest in June overwhelmingly drew peaceful, festival-like crowds, Trump and his allies have increasingly criticized the follow-up event and described the protesters as terrorists, Hamas supporters, and far-left agitators. The accusations, made without presenting any evidence, have made some observers anxious.

“Even just what lawmakers are saying is very different this time around,” Klosowski said. “I’m a little more worried this time than I was last time.”

Plans for “No Kings” protests have drawn the attention of at least one of the U.S. government’s domestic intelligence “fusion centers” established after the 9/11 attacks, according to an alert obtained by Property of the People.

The document from the Central California Intelligence Center identified Sacramento, Fresno, and Stockton among dozens of “No Kings” protest sites.

Noting that while the protests were billed as “nonviolent action,” the center said additional intelligence reports were being planned on the rallies. The center did not immediately respond to a request for comment.

The National Fusion Center Association did not directly address questions about October 18 plans, but referred Reuters to a 2011 federal document, listing recommendations for law enforcement agencies regarding “First Amendment-Protected Events.”