House Republicans on Thursday will try to reauthorize a key but controversial counterterrorism tool, despite a split among lawmakers that could end up sinking the bill.

Dozens of members are expected to vote for a bill-gutting amendment to underlying legislation reauthorizing Section 702 of the Foreign Intelligence Surveillance Act, which allows intelligence officials to spy on communications of non-citizens outside of the U.S.

The amendment, sponsored by Reps. Justin Amash, R-Mich. and Zoe Lofgren, D-Calif., is named the USA Rights Act, and it would strictly limit the way intelligence officials can collect communications involving Americans, going far beyond the moderate limitations to the program included in the underlying bill.

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For example, Amash's plan would end “abouts” collections, which go beyond searches based on the sender fields in emails and allow searches of the contents of messages. It would also stop so-called reverse targeting of Americans who are caught up in the surveillance of foreign communications, and bolster requirements for search warrants.

Passage of the amendment would essentially kill the underlying bill, which reauthorizes the spy tool with more moderate changes written by the Intelligence and Judiciary Committees. Procedurally, passing Amash's language would morph the bill into a version he and his supporters like, at which point GOP leaders would probably yank the bill from the floor, or if it somehow passed, the Senate would be unlikely to take it up in that form.

The House Freedom Caucus and other Republicans have endorsed the Amash amendment, thus splitting the GOP on the bill. And many Democrats are also expected to back the Amash provision.

“There is a big divide on our side,” Rep. Gerry Connolly, D-Va., who backs the Amash amendment, said Wednesday. “And certainly on [the Republican] side. It puts the bill in jeopardy. I think it falls short.”

The House voted to advance the legislation on Wednesday by approving debate rules, but the real battle comes Thursday, when the House votes first on the Amash amendment, and if that fails, the underlying bill.

Republicans and Democrats who back the underlying bill say the Amash amendment is unnecessary because reforms have been added to boost privacy protections, including stronger requirements for search warrants. The Amash amendment is simply an attempt to kill the bill, proponents of the underlying legislation said Thursday.

But the reforms offered in the underlying legislation were not enough for many lawmakers, who are also receiving pressure from outside groups including FreedomWorks and the ACLU, which have declared the spying tool unconstitutional.

Rep. Jim Sensenbrenner, R-Wis., a senior member of the Judiciary Committee and its former chairman, said the underlying bill includes new warrant requirements that excludes many of the kinds of searches performed by intelligence officials, sweeping in millions of innocent emails sent by Americans.

“The loopholes in this bill are too great to ensure proper protection,” Sensenbrenner said.

Rep. Mark Meadows, R-N.C., chairman of the House Freedom Caucus, said that while his faction endorses the Amash amendment, he expects Republicans will provide enough votes to pass the legislation.

Republican leaders spoke out against the Amash amendment in a closed-door meeting with rank and file lawmakers on Tuesday.

“In the end, I’m not seeing a whole lot of nervousness on behalf of the whip team,” Meadows said. “The whip team is probably giving them pretty good assurances that they are going to get a FISA reauthorization without changes.”

If the House kills the Amash amendment and passes the underlying bill, Senate Republicans said they’ll move it to the floor ahead of a Jan. 19 deadline.

Senate Majority Whip John Cornyn, R-Texas, said in that case, the Senate is likely to pass the measure, which would clear it for President Trump’s signature. The Senate may consider the measure as a standalone bill or attach it to a bill to temporarily fund the government, which is expected next week ahead of a Jan. 19 government funding deadline.

But there is also opposition in the upper chamber. About two dozen lawmakers in both parties have signed onto legislation offered by Sen. Ron Wyden, D-Ore., which mirrors the Amash bill.

“Politicians who support broad, unchecked government surveillance authorities are once again rushing to approve a sweeping program at the expense of Americans’ personal liberty and constitutional rights,” Wyden said of the House underlying measure in an opinion piece published on thecipherbrief.com.