Republican Sen. Susan Collins of Maine said Monday evening that she aims to alter the GOP tax reform bill to provide more middle-class tax relief by keeping the top income tax rate where it is and perhaps by not lowering the corporate tax rate to the 20 percent sought by GOP leadership.

"It’s premature for me to take a position on the bill," Collins told reporters at the Capitol. "I would like to see more of the tax relief skewed to middle-income and lower-income families."

Senate Majority Leader Mitch McConnell, R-Ky., can lose only two Republican votes and pass the tax legislation without Democratic help. Collins is thought to be one of the Republicans whose vote is most in question.

She said Monday that she would like to see the bill changed to forgo the cut in the top individual income tax rate from 39.6 percent to 38.5 percent and for that tax revenue to be dedicated to preserving some of the state and local tax deduction, which is targeted for elimination in the version of the bill working its way through the Senate Finance Committee this week. Or, she said, the funds could be redirected to making the bill's enlarged child tax credit refundable, meaning that the Treasury would pay it to families even if they had no income tax liability.

Both those changes would direct more of the tax cuts to middle-income and lower-income families.

Both also could be pursued by easing up on Republican ambitions for lowering the corporate tax rate from 35 percent, Collins suggested.

"I also think we should take a look at whether we really need to go all the way to 20 percent on the corporate rate," she said. A 21 percent rate could allow enough revenue to ensure that families further down the income spectrum received tax cuts, she said.

President Trump's advisers have said that the 20 percent rate is one of the few non-negotiable items in the tax package. Trump originally wanted a corporate tax rate of 15 percent.