Full page ads in Jewish newspapers and banners popping up on Jewish community websites made it clear that Senator Joseph Lieberman, once an icon of Jewish politics, is now at odds not only with his former Democratic Party, but also with his own Jewish community.

Mr Lieberman, who now defines himself as an independent but is part of the Democratic caucus, holds the key vote in passing President Obama’s ambitious healthcare reform plan. Being the 60th vote on the floor, Mr Lieberman’s vote is crucial, since falling short of a 60-vote majority would allow Republicans to filibuster the bill and derail the entire legislative process.

Mr Lieberman, a fiscal conservative who has broken with Democrats in the past on many issues, opposes the proposed bill and has refused to support it unless it is stripped of any measure that could increase government involvement in running the country’s failed healthcare system.

This approach has made the Connecticut senator the epicentre of attention and political pressure. Mr Lieberman’s opponents accused him of serving the interest of big medical insurance companies that are based in his home state and of trying to use his position as the deciding vote to gain political capital.

Activists within the Jewish community have been among Mr Lieberman’s harshest critics. “Senator Lieberman, what is it that your conscience tells you?” asked the ads in Jewish newspapers, signed by dozens of Connecticut-based rabbis and clergy of other faiths.

Rabbi Ron Fish, who organised the appeal, said it was Mr Lieberman who first invoke faith and conscience in explaining his opposition to the proposed healthcare reform bill.

Local rabbis felt they should have a say on the issue as well. Rabbi Fish joined an interfaith group prayer vigil last month outside Mr Lieberman’s home and intends to keep up the pressure as long as the senator refuses to allow the healthcare bill to pass.

For the Jewish community, healthcare reform has been a major cause and rallying issue. Citing the biblical and halachic command to take care of the sick and help the needy, national and local Jewish groups have lobbied in favour of reforming America’s healthcare system, which currently leaves 47 million people without any coverage. The cause was taken on forcefully by the Reform Movement, which is the biggest Jewish denomination in the US, and by national public policy Jewish organisations and Jewish women’s groups.

Mr Lieberman and his supporters accuse critics of misrepresenting his opposition. According to Mr Lieberman, he strongly supports the need for reform healthcare and agrees to most components of the bill. However, he believes that it could open the door to uncontrolled government spending.

Fingers are also being pointed at Mr Lieberman’s wife, Hadassah, who has done work for firms involved in lobbying for medical insurance and drugs companies that are at risk of losing income if the bill passes.