A powerful electronic surveillance tool widely used by US intelligence agencies abroad -- but criticized by civil liberties organizations -- is set to lapse at midnight Friday into Saturday due to inaction by the US Senate.

"We're still trying to see if there's a path to getting this bill done quickly, but disagreements remain on how to proceed," Senate Democratic Majority Leader Chuck Schumer said.

The expiration is expected to be short-lived, as senators are expected to be in session over the weekend to vote on its renewal.

The program enables US intelligence agencies to conduct electronic surveillance programs without seeking a judicial warrant.

In particular, it allows them to sweep up communications, including phone calls and emails, of non-Americans anywhere outside of US territory. That includes communications from US citizens to foreigners targeted for monitoring.

The authority under Section 702 of the Foreign Intelligence Surveillance Act (FISA) has been denounced by privacy and civil liberties advocates.

It passed the House last Friday, but its renewal is still the subject of fierce debate.

Former president Donald Trump, who wants to unseat Joe Biden in elections this fall, got involved in the negotiations by urging lawmakers last week to "Kill FISA."

"It was illegally used against me, and many others. They spied on my campaign!!!" Trump wrote, without proof, on his Truth Social platform.

In mid-December, a senior White House official had argued for its extension, saying that given threats and conflicts around the world, including in Ukraine, the Middle East and with China, "this would be a very bad time to disarm unilaterally."