Washington (CNN) - There's been a ton of liberal anger this week focused on Independent Sen. Joe Lieberman - who those on the left considered the main obstacle to the Democrats' efforts to pass a health care reform bill in the Senate by Christmas.
But now, an Independent senator from the progressive side of the Democrats' coalition could threaten passage of a reform bill.
Bernie Sanders of Vermont says he may vote against the legislation. The Independent from Vermont, who like the moderate Lieberman caucuses with the chamber's 58 Democrats to give the party a 60 seat filibuster-proof majority, says he has major problems with the bill.
"I have made it clear that, at this point, it is not for sure that I will vote for that bill unless it becomes significantly better," the first-term senator and former socialist mayor of Burlington, Vermont, told CNN's Wolf Blitzer on "The Situation Room" Wednesday evening.
Sanders, who favors a single payer health care system, explained to Blitzer why he has problems with the current bill in the Senate: "Right now, with the withdrawal of the public option, what that means is that the private insurance companies are not going to have any competition. And they are going to be able, it seems to me, to be able other continue to raise their rates as high as they want, which is what they have been doing for many years. So, what I am right now doing is working with the White House, working with the Democratic leadership to try to make this bill as strong as I can."
Following his interview with CNN, Sanders appeared to go bit further in his opposition, telling Fox Business Network that "as of this point I am not voting for the bill."
Earlier Wednesday, Sanders withdrew from consideration his amendment that called for a single-payer healthcare system after Republican Senator Tom Coburn of Oklahoma forced the entire 767 page measure to be read aloud in the chamber, in a move to stall and defeat the Democrats health care reforms.
- CNN's Paul Steinhauser contributed to this report