The Blue Dog Democrats (Democratic House members more fiscally conservative than the rest of the party) have said they want "significant changes before they can support a sweeping health care overhaul," according to the Associated Press. In particular, the Dogs want changes that will benefit rural communities, doctors and, in particular, hospitals. The Blue Dogs (there are 52 of them in the House) say they can't vote for the health care reform bill that is currently being discussed.
You can read the letter from the Blue Dogs here. The letter says any health care reform needs to be cheaper — that or savings need to be found in the current system. They say the current bill "fails to include adequate structural changes that will succeed in lowering costs and increasing value." You can't just add new people to an overly expensive system.
In particular, the Blue Dogs demand "rural health equity." In a letter to House Democratic and Republican leaders, the Dogs write: "Rural communities face unique challenges in delivering health care, and our reform efforts must not overlook them. The short-term extensions of rural provisions included in the discussion draft are critical, but we must not fail to address the underlying problems and inequities that plague rural providers. A strong rural package is critical to our support."