Congress is set to take up the reauthorization of a divisive program that lets U.S. spy agencies pore over foreigners' calls, texts and emails, with supporters like President Donald Trump saying it has saved lives while critics point to longstanding concerns about warrantless surveillance of Americans.

A key provision of the Foreign Intelligence Surveillance Act permits the CIA, National Security Agency, FBI and other agencies to collect and analyze vast amounts of overseas communications without a warrant. It incidentally sweeps up the conversations of any Americans who interact with those foreigners targeted for surveillance.

The program expires Monday, and critics want changes, including a requirement for warrants before authorities can access the emails, phone calls or text messages of Americans. They also want limits on the government's use of internet data brokers, who sell large volumes of personal information gleaned online, offering the government what critics say amounts to an end-run around the Constitution.

Despite bipartisan criticism, the chances of significant reforms dropped when Trump announced his support for the program's renewal, saying it had proven its worth in supplying information vital to recent U.S. actions in Venezuela and Iran.

"The fact is, whether you like FISA or not, it is extremely important to our military," Trump said on Truth Social Tuesday.

U.S. authorities say the program, known as Section 702 of the law, is vital to national security and has saved lives by uncovering terror plots. Critics question what they call a dangerous infringement on civil liberties and privacy.

In a Truth Social post, Trump said a different FISA provision was used to spy on his 2016 campaign but that he supported Section 702's renewal despite misgivings that political adversaries could use parts of the law against him in the future. He called on lawmakers to extend the foreign surveillance program for another 18 months.

"My administration has worked tirelessly to ensure these FISA reforms are being aggressively executed at every level of the Executive Branch to keep Americans safe, while protecting our sacred Civil Liberties guaranteed by our Great Constitution," Trump wrote.

Trump is a longtime critic of the nation's intelligence services and was once opposed to Section 702 before he reversed himself. "KILL FISA" Trump posted on social media in 2024, when the provision was last reauthorized.

Trump isn't the only one-time critic to change their mind: Director of National Intelligence Tulsi Gabbard sponsored legislation to repeal Section 702 as a Hawaii congresswoman but now supports it after being tapped to coordinate the nation's 18 intelligence agencies.

Gabbard says new protections added since her time in Congress helped change her mind.

In addition to a requirement for a warrant to access Americans' data, critics also want greater protections on how the FBI or other agencies can search communications and how that is reported to the public.