Democrats say House Republicans may have to vote again on their Obamacare repeal bill before sending it to the Senate, citing among other things an obscure provision that affects health care for Native Americans.

Republicans dismissed the problem as hypothetical, but taking another vote is the last thing the House GOP wants to do, after barely managing to pass the bill on May 4 with a razor-thin 217-213 margin after weeks of negotiations with dissidents in their own party. House Speaker Paul Ryan still hadn’t sent the bill to the Senate by Monday afternoon, as lawmakers await a ruling on whether the measure is eligible for a streamlined Senate procedure allowing the GOP to pass it with a simple majority.

The Senate parliamentarian’s decision on that question could come this week, possibly as soon as late Monday.