Supporters of the liability shield, including the White House, have argued that such protection is necessary to jump-start a domestic vaccine industry that has slowed in recent years over liability concerns.

The House has approved the conference report, produced by negotiations between the House and the Senate, by a vote of 308-106 yesterday.

In the Senate the bill faces a far tougher road. Democrats there have threatened to filibuster over what they see as unrelated "sweetener" provisions, most notably authorization for oil drilling in the Artic National Wildlife Preserve that was included for Sen. Ted Stevens, R-Alaska.

Consumer and civil justice groups in a letter to senators said the provisions would provide "never-before-seen" legal immunity to the drug industry, even for practices that could injure or kill consumers or health care workers.

The groups signing the letter included the Alliance For Justice, Center For Justice And Democracy, Consumer Federation Of America, Public Citizen, USACTION and U.S. PIRG

Their letter said that while drug manufacturers would be given protection, first responders and others injured by vaccines or medical devices get little or no protection, even if injured through negligent or reckless conduct.

"Drug companies," the letter said, "will only be held responsible if there is clear and convincing evidence that the company had actual knowledge the product would kill someone. This is a near impossible standard, which would mean that drug companies will not be accountable for reckless or grossly negligent conduct, even in the manufacturing process."

The conference report was due to be considered today on the Senate floor. The 45-page immunity clause was added without any floor debate in either house.

According to the letter, the immunity from liability is so broad that it "could apply to common drugs like Tylenol and Advil" if approved for use by the Secretary of Health and Human Services in any health emergency.

The groups urged Senators to vote "no" on the conference report unless the liability immunity provision is deleted and pointed out that the bill offers no guarantee that victims will be compensated in any way for injury or death: "Individuals who may suffer serious illness or death as a result of taking a vaccine or other countermeasure are given no assurance of compensation."