A bipartisan group of senators told congressional leaders Thursday they will try to block reauthorization of the Patriot Act to protest the elimination of Senate-pushed protections against "unnecessary and intrusive government surveillance" in a House-Senate compromise.

"If further changes are not made, we will work to stop this bill from becoming law," GOP Sens. Larry Craig, John Sununu and Lisa Murkowski and Democratic Sens. Dick Durbin, Russ Feingold and Ken Salazar said in a letter to the Senate Judiciary and Intelligence committees.

This came a day after House-Senate negotiators crafted a tentative compromise to make most provisions of the existing law permanent, and set new seven-year sunsets for rules on wiretapping, obtaining business records under the Foreign Intelligence Surveillance Act (FISA) and new standards for monitoring "lone wolf" terrorists who may be operating independent of a foreign agent or power.

Congress is facing two deadlines: lawmakers want to leave before the end of the week for Thanksgiving, and more than a dozen provisions of the Patriot Act expire at the end of the year if Congress doesn't renew them.

The Republican-controlled House hopes to approve the compromise on Friday, and Senate Majority Leader Bill Frist, R-Tenn., told senators Thursday they will have to address the legislation "before we leave."

But Feingold, D-Wis., the only senator to vote against the original Patriot Act in 2001, said the compromise's opponents have several different tactics they can use to stop the bill in the Senate.

"I've let my colleagues know that I intend to take as many of those options as I can in order to try to get this bill redone," Feingold said Thursday. "They said, 'I understand,' but I don't know whether that means they're going to change the bill or whether they want to just go through this whole process."

The six senators — Feingold; Craig, R-Idaho; Durbin, D-Ill.; Sununu, R-N.H.; Salazar, D-Colo.; and Murkowski, R-Alaska — were the sponsors of legislation earlier this year that would have tempered the powers of the Patriot Act, the post-Sept. 11 law that expanded the government's surveillance and prosecutorial powers.

They complained that the House-Senate compromise now being considered takes back some civil liberty protections that senators had agreed to, including changing a Senate requirement that the government inform the targets of a "sneak and peek" search warrant within seven to 30 days.

"Sneak and peek" search warrants allow police to conduct secret searches of people's homes or businesses and inform them later.

The compromise also removed a Senate provision that would have mandated judicial reviews when authorities used Patriot Act powers to search financial, medical, library, school and other records, the six senators said.

"We cannot support a conference report that would eliminate the modest protections for civil liberties that were agreed to unanimously in the Senate," they said.

Senate Judiciary Committee Chairman Arlen Specter, R-Pa., said he was working to address some of the group's complaints. The compromise is not official and has not been signed by any of the 34 negotiators.