RICHMOND — Two dozen Democratic members of the Virginia House have vowed to vote against the budget this year unless the General Assembly agrees to expand Medicaid — and some members of the caucus are pushing to conditionally tie support for a transportation package to Medicaid also.

In a letter dated Thursday to the House and Senate finance committee chairmen, 24 delegates said they backed the Senate version of pushing state flexibility and reform while also moving ahead under the federal Affordable Care Act to expand health insurance coverage for low income people under the federal program. The letter says the House version poses hurdles that could hold up Medicaid expansion 18 months at a cost of $3 billion.

“Our economy cannot lose out on $3 billion,” the letter to Del. Lacy E. Putney (I-Bedford) and Sen. Walter A. Stosch (R-Henrico) said. “And we simply cannot support a budget that doesn’t expand Medicaid.”

Del. Patrick A. Hope (D-Arlington), one of the signatories, said there also is a growing movement within the Democratic ranks to block a transportation funding package unless Medicaid is expanded.

“That sentiment is growing,” Hope said.

But Republicans rejected any connection between the two.

“We did not want linkage between transportation and Medicaid. I’d be very disappointed to hear any group starting to make that linkage,” Sen. Majority Leader Thomas Norment (R-James City) said.

Some Democrats also rejected a tie between the legislation, creating some dissension in the caucus.

“There are some people who believe it’s an opportunity to get Medicaid expansion simultaneously by holding out on the transportation bill,” said Del. Onzlee Ware (D-Roanoke City). “Personally, I disagree with that. I honestly think [transportation] it’s a reasonable compromise and if we don’t do it this year, we won’t get it for years.”

Earlier Thursday, Gov. Robert F. McDonnell urged budget negotiators not to open the door to Medicaid expansion until reforms to the federal program have been approved and implemented.

In a letter to the heads of the Senate Finance and House Appropriations committees, McDonnell (R) said Medicaid spending, which has grown 1,600 percent in Virginia in the past 30 years, presents a huge burden to the state even without expansion.

“Please understand that I cannot and will not support consideration of an expansion of Medicaid in Virginia until major reforms are authorized and completed, and until we receive guarantees that the federal government’s promises to the states can be kept without increasing the immoral national debt,” McDonnell wrote. “To do so would be irresponsible and place crushing financial burdens on future governors and legislatures. The country is broke, and I will not support policies that make it worse.”

McDonnell sent the letter as House and Senate budget conferees are attempting to work out a compromise on amendments to the remainder of the current two-year budget, which began in July.