"I'm still looking at the bill, but I have a lot of concerns about it," she told Yahoo News. "I'm not crazy about it."

Two committees are marking up their sections of the House ObamaCare repeal proposal on Wednesday. The bill, known as the American Health Care Act, would dismantle major provisions of the Affordable Care Act and cut off federal funding for Planned Parenthood.

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Collins argued that lawmakers should "slow down," noting they didn't have the Congressional Budget Office analysis of the plan, which would detail the cost of the bill and its impact on the number of insured individuals.

"It was wrong of President Obama to push through the bill without allowing for full amendments," she said. "I don't want to see us make that same mistake."

A group of centrist Republicans has also raised concerns about what happens to ObamaCare's Medicaid expansion.

Collins added on Wednesday that she has "concerns" about the Medicaid language, as well as the decision to include cutting off Planned Parenthood in the bill.

Republicans, who have a 52-seat majority, can only afford to lose two GOP senators if they want repeal language to clear the upper chamber. Republicans want to vote on the repeal bill before they leave town for the two-week Easter recess in early April.

Any combination of the conservatives and more moderate factions who have raised concerns about the House bill would be able to kill any repeal bill that they opposed.

Republicans have signaled this week that they expect the House repeal legislation will undergo revisions before it reaches the Senate.

Collins, echoing her colleagues, suggested that the House bill could potentially improve before she has to cast a vote.

"I do want to emphasize that it's still a work in progress," she told Yahoo News. "The bill that was released this week is far better than the bill that we were briefed on the week before."