Washington ? A bipartisan group of a half-dozen senators slammed the brakes on efforts to extend the life of the USA Patriot Act on Thursday, charging that a compromise version being debated in a conference committee does not do enough “to protect innocent people from unnecessary and intrusive government surveillance.”

In a letter to the Senate Judiciary and Intelligence committees, three Republicans joined three Democrats in describing the bill as “unacceptable.” They added that “if further changes are not made, we will work to stop this bill from becoming law.”

They issued their challenge after conference negotiators had hammered out a compromise to make permanent most provisions of the Patriot Act. The statute is set to expire Dec. 31.

Officials on both the House and Senate side said conferees are working toward an agreement that would get the six out of 10 votes needed to move the bill back to the House and Senate. Once that happens, it is not possible to amend the bill again.

The conference report would make 14 of the law’s 16 provisions permanent and would add seven-year expiration dates for one provision that gives the FBI access to personal and business information and another that allows it to wiretap all of a suspect’s telecommunications.

The critics are Republicans Larry Craig, R-Idaho, John Sununu, R-N.H., Lisa Murkowski, R-Alaska, Richard Durbin D-Ill., Russell Feingold E-Wis. and Ken Salazar D-Colo.