House Republicans barely managed to pass their Obamacare repeal bill earlier this month, and they now face the possibility of having to vote again on their controversial health measure.

House Speaker Paul Ryan hasn’t yet sent the bill to the Senate because there’s a chance that parts of it may need to be redone, depending on how the Congressional Budget Office estimates its effects. House leaders want to make sure the bill conforms with Senate rules for reconciliation, a mechanism that allows Senate Republicans to pass the bill with a simple majority.

Republicans had rushed to vote on the health bill so the Senate could get a quick start on it, even before the CBO had finished analyzing a series of last-minute changes. The CBO is expected to release an updated estimate next week.