The total cost of the extenders bill scheduled to be unveiled this week has also increased, to $226 billion.
The ballooning cost is causing heartache for vulnerable House members and moderate senators.
The lobbying source added that the bill is unlikely to be released before Wednesday as members keep close tabs on the results of Tuesday’s elections, which may affect lawmakers' appetite for passing measures that add to the deficit.
Senate Finance Committee Chairman Max Baucus (D-Mont.) this afternoon said the situation was “fluid.”
Asked about the duration of the change to the Medicare Sustainable Growth Rate formula (SGR) that's going to emerge, he said: “SGR has got to be extended. These things are all fluid. It's down to policy and votes.”