Sen. Rand Paul, R-Ky., on Wednesday threatened to filibuster any legislation that includes long-term reauthorization of government's foreign intelligence program.

I will actively oppose and filibuster any long term extension of warrantless searches of American citizens — Senator Rand Paul (@RandPaul) December 20, 2017

Paul and his fellow Republican Sen. Mike Lee of Utah both vowed to vote against any spending bill that would reauthorize Section 702 of the Foreign Intelligence Surveillance Act, which allows the National Security Agency to monitor foreign targets without a warrant, even when those communications are with American citizens.

The House released a bill on Tuesday that includes a four-year extension to the program, which is currently due to expire at the end of this year.

"This bill is an eleventh-hour attempt to sneak an unchecked warrantless surveillance program through Congress," Sen. Ron Wyden, D-Ore., told The Hill in a statement.

"The legislation posted late yesterday is a clear step backward for Americans' rights. It does nothing to check the warrantless backdoor searches of Americans' communications," he added.

"The bill also fails to codify the current prohibition on 'abouts' collection, in which communications entirely among innocent Americans can be swept up if they reference a target's email address."