© CNN 2009

Simmering liberal angst over the Senate health care bill threatened to boil over Thursday as a critical labor union threatened a new fight over provisions that were dropped to attract more moderate supporters. 

The warning came shortly after a top Senate progressive indicated he is not prepared to back the bill as currently drafted. 

Senate Democratic leaders also faced continuing problems with social conservatives in their ranks. A key moderate continued to warn that Majority Leader Harry Reid's bill does not do enough to bar taxpayer-funded abortions. Read more.