House Republicans are racing to finalize their tax reform proposal before its much-anticipated rollout Wednesday morning. But so many key details have yet to be finalized that some congressional sources worry the unveiling may have to be postponed.

House Ways and Means Committee members spent all Tuesday holed up in conference rooms trying to iron out last-minute disagreements. Senior committee staff worked through the night Monday and were expected to do the same on Tuesday.

House Ways and Means Chairman Kevin Brady (R-Texas) often says Republicans have spent more than half a decade working on their tax bill. But not 24 hours before the bill’s big reveal, lawmakers had yet to settle on one of the most sensitive questions of all: How to pay for their proposed $5.5 trillion in tax cuts, since any major revenue-generator is certain to antagonize some powerful lobby or group of lawmakers who could defeat it.

“Our plan is to release the bill tomorrow,” Brady told reporters Tuesday afternoon, leaving himself some wiggle room. Asked if Wednesday’s release would be legislative text, Brady responded: “When we release the bill, it will be text.”