Sen. Susan Collins Susan Margaret CollinsMcConnell locks down key GOP votes in Supreme Court fight Most Americans think winner of election should pick next Supreme Court justice: poll Murkowski: Supreme Court nominee should not be taken up before election MORE (R-Maine) said on Friday she has serious concerns about the latest GOP bill to repeal and replace ObamaCare as Republicans prepare to vote on the legislation next week.

“The premiums would be so high they would be unaffordable,” she said, referring to the cost for individuals with pre-existing health conditions.

If Collins votes against the bill, GOP leadership will be left with no room for error if they want to get their last-ditch ObamaCare repeal bill through the Senate next week.

Republicans have 52 seats. They need 50 senators to support the bill, which would require Vice President Pence to break a tie, under the special budget rules being used to avoid a Democratic filibuster.

Those rules expire at the end of the month, meaning after next week Republicans would need 60 votes to pass an ObamaCare repeal.

Republicans are taking heavy fire over a provision of their bill that would allow states to repeal rules aimed at protecting individuals with pre-existing conditions.

Cassidy, however, has denied that his bill would hurt people with health problems, noting states would have to be able to tell the federal government how they would provide "adequate and affordable" coverage.

But experts argue there is no clear definition in the bill of what “adequate and affordable” care means.