Senate Republicans are voting Thursday and possibly Friday to amend their tax bill, and are hoping to shore up support among their own members in order to ensure the 50 votes needed to pass their sweeping tax overhaul.

Senate Majority Leader Mitch McConnell, R-Ky., appears to be close to having the votes to pass the bill, but some members of his conference want changes to the bill. So far, a handful of members have made public demands. Here’s what they want:

Bob Corker of Tennessee and James Lankford of Oklahoma

The self-professed deficit hawks in the GOP conference are worried that the roughly $1.5 trillion tax cut might not spur economic growth the way Republicans hope it will, and that the federal debt will soar as a result.

Corker and Lankford have been working on a “debt trigger” they want added to the bill. The details of the mechanism were still being worked out Wednesday night, but the basic idea is that tax cuts would be scaled back if, after a period of time, federal revenues fell below projections.

Corker has suggested that he will vote against the bill if he thinks it will add to deficits, meaning that the trigger is needed for his support. But many outside conservatives don’t like the idea, and some within his conference are wary of it.

Ron Johnson of Wisconsin and Steve Daines of Montana

Johnson has led the charge to increase the size of the bill’s tax cuts for non-corporate businesses, such as partnerships and sole-proprietorships, to put them on an equal footing with C corporations, which are slated to get a tax rate of 20 percent.

He and Daines said Wednesday that they had received a commitment from leadership to boost the tax break for pass-through businesses. Johnson is also planning an amendment to further increase those cuts, at the expense of a tax break for corporations.

Marco Rubio of Florida and Mike Lee of Utah

Rubio and Lee have said the bill doesn’t provide enough tax relief to working families. They will offer an amendment to make the increased child tax credit in the bill available to more low-income families by making it refundable against payroll tax liability and indexing it to inflation.

Their amendment, though, would pay for that expansion of the child tax credit by setting the corporate tax rate at 22 percent, rather than the 20 percent currently envisioned.

That trade would set up a conflict with the White House, which has said that a 20 percent corporate tax rate is one of President Trump’s red lines.

One potential dynamic to watch would be whether Democrats would vote in favor of the Rubio-Lee amendment, even if they would then vote against the underlying bill.

Susan Collins of Maine

Collins, long thought of as a “maybe” on the tax bill because she is the furthest left in the Senate GOP conference, said Wednesday that she favored tax cuts but would offer a few high-priority amendments that would likely have to pass to earn her vote.

The biggest one would match the House of Representatives in creating a deduction of up to $10,000 for state and local property taxes. The current version of the Senate bill completely eliminates state and local deductions.

Collins said she had a commitment from leadership to include the property tax deduction, something that House leadership has also promised to members from high-tax blue states. Collins’ amendment would pay for the break by raising the corporate tax rate from 20 percent to 21 percent.

Wildcards

Other Republicans may quietly harbor reservations about the tax bill. Those could surface Thursday or Friday as the bill is revised by leaders and then through unlimited amendments on the Senate floor.