Sen. Joe Lieberman reaffirmed his pledge Wednesday to withhold his vote for the Senate's sweeping health care reform bill if it includes a so-called "public option," saying a government-run plan is "unnecessary" and threatens to drive up costs for taxpayers. 

"It's not free," the Connecticut senator told Fox News on Wednesday.

Lieberman, an Independent Democrat, said a day earlier that he would back a Republican filibuster against Senate Majority Leader Harry Reid's health care reform bill if a government-backed insurance plan remains in the package. He warned Wednesday that the plan would have several negative side effects. 

"Someone's going to have to pay for it and you bet it's going to be the taxpayer," Lieberman said, adding that a government-run insurance plan will drive up premiums -- despite claims from some Democrats that it would lead to an improved system because it will create healthy competition.

Lieberman's opposition is a blow to Reid and signals that the Democratic leader does not yet have the votes to advance the bill. While Reid needs just 51 votes to pass the package, he needs 60 votes to crush a filibuster.

Lieberman said he would vote with Democrats on a motion to begin floor debate on the Senate's bill, but indicated that he would not vote for cloture -- a motion that would end the debate, allowing the bill to go before the Senate for a vote.

Despite his opposition to a government-run insurance program, Lieberman suggested the proposal could be revisited "three to four years" from now "if other reforms are not working."

"But I think they will," he added.