The House Freedom Caucus announced Thursday it will oppose reauthorizing the FISA Amendments Act, the legal basis for U.S. surveillance programs, without "substantial" reforms to the law.

Section 702 of that law has come under fire recently after revelations that this provision was used to capture communications of President Trump and his transition team as it had conversations with foreign officials. Under the law, this kind of incidental collection of information from U.S. citizens occurs, but U.S. citizens caught up in that surveillance are usually masked, unless intelligence officials decide there is a good reason to unmask that person.

Republicans argue the outgoing Obama administration unjustifiably unmasked and then leaked conversations involving Trump's team, which has created demands among conservatives for reform.

"Government surveillance activities under the FISA Amendments Act have violated Americans' constitutionally protected rights," the Freedom Caucus board said in a statement. "We oppose any reauthorization of the FISA Amendments Act that does not include substantial reforms to the government's collection and use of Americans' data."

The Freedom Caucus has not said what specific reforms it will pursue.

But Rep. Thomas Massie, R-Ky., who is close with the Freedom Caucus despite not being a formal member of the conservative group, has proposed for three years in a row an amendment to Section 702 to prohibit warrantless searches of government databases for information on U.S. citizens.

Other changes to the law proposed by civil liberty advocates include narrowing the pool of foreigners that the government can legally target for surveillance, thereby limiting Americans who could be caught in the web, to include only those who may pose a threat to U.S. interests.

Congress also could require the circle of officials who can authorize unmasking to be smaller, and tighten the constraints on doing so.

Section 702, which expires Dec. 31 along with other portions of the law, has been reauthorized in past years despite hand-wringing from libertarians and some Democrats. This year's effort is more difficult given the political fighting over the law.

In April, numerous news outlets reported that Susan Rice, former President Barack Obama's national security adviser, sought the identities of people close to Trump whose communications were captured after the election in surveillance of foreigners by U.S. spy agencies.

Intelligence and national security experts say that it's both legal and normal for someone in Rice's position to unmask people.