“We must have the opportunity to read and understand the final bill before we vote. It’s irresponsible to do otherwise,” added conservative Rep. Justin Amash (R-Mich.) in a tweet Thursday night.

Republicans on Thursday night announced that they would make some significant changes to the bill with the intention of winning over conservatives.

The most prominent of those changes is to repeal ObamaCare’s essential health benefits, which mandate which health services an insurance plan must cover, including areas like mental health, prescription drugs, and maternity care. The GOP will also add $15 billion to a “stability fund” to the bill in order to provide mental health and maternity coverage, which will be paid for by keeping ObamaCare’s 0.9 percent Medicare tax on high earners for six years.

Repealing the essential health benefits could have far-reaching consequences for the legislation and for the U.S. healthcare system, but the CBO will not have time to release an analysis of the change before the vote on Friday.