The conservative House Freedom Caucus voted Monday night to oppose an ObamaCare repeal bill if it does not go as far as the repeal measure that passed in 2015, drawing a line in the sand that could complicate Republican repeal efforts.

Conservatives have been pushing for the 2015 repeal bill, which kills the core elements of the law including its subsidies, taxes, mandates and Medicaid expansion, to be brought up again. But the move Monday night to oppose an effort if it falls short of that bill is a significant new development.

Some more moderate Republicans are uneasy with repealing all of ObamaCare's taxes, and especially with repealing the Medicaid expansion. But if repeal of those areas is weakened, the Freedom Caucus now says it would oppose the bill.

"If it's less than 2015, we will oppose it," Rep. Mark Meadows (R-N.C.), the chairman of the Freedom Caucus, said after exiting the meeting.

More moderate Republicans from states that expanded Medicaid are wary of losing extra federal funds if the expansion were repealed, and of the possibility that their constituents could lose coverage.

The Freedom Caucus is still pushing for replacement to pass at about the same time as repeal, though it wants replacement to be in a separate bill, and has indicated at least some flexibility on the timing of replacement.

"We're encouraging a replacement at the same time," Meadows said Monday.

House Republican leadership is looking to include some elements of replacement in the repeal bill: expansion of health savings accounts, a tax credit, high-risk pool funding and Medicaid changes.

Meadows said Monday that the Freedom Caucus does not oppose adding pieces of replacement to the repeal bill on principle, but it depends on what the pieces are.

He expressed openness to the possibility of a provision on Health Savings Accounts, but wariness of the idea of adding a tax credit. Opposition to a tax credit also could be a major hurdle, given that tax credits are at the center of most Republican replacement plans.