Republican Sen. Susan Collins told Bloomberg that she has two stipulations to support the GOP's tax bill.

Collins wants the estate tax to remain and no tax cuts for people making $1 million a year.

The demands could throw a wrench in Republican tax reform negotiations.

Sen. Susan Collins on Monday said she would have two demands to support the forthcoming Republican tax reform bill.

Collins, a moderate member of the Senate GOP conference, told Bloomberg's Sahil Kapur on Monday that the tax plan should not repeal the estate tax or change tax rates on people making more than $1 million a year.

"I do not believe that the top rate should be lowered for individuals who are making more than $1 million a year," Collins told Bloomberg. “I don’t think there’s any need to eliminate the estate tax."

The estate tax currently applies to inheritances of more than $5.49 million, and that limit will be increased to $5.60 million for individuals in 2018. Despite Republicans' insistence that the repeal is aimed at small businesses and family farms, very few of either pay the tax.

The demands from Collins are important, since Republicans only control 52 seats in the Senate. While the tax bill is set to go through the budget reconciliation process, meaning it only needs 50 votes to pass, Republican leaders can only afford to lose two members of their conference.

Collins voted against various Republican Obamacare repeal bills over the summer and has made it apparent that she is not afraid to vote against leadership's wishes.

Already a handful of Republican senators, most notably Sen. Bob Corker, have raised concerns about the plan's potential effect on the federal deficit. Sen. Rand Paul said he also had reservations about the distribution of the benefits from the plan.

Despite the demands, Collins told Bloomberg that she hopes to vote for the tax package.

"I hope very much to be able to support a tax reform package," Collins said, but added she can't guarantee she will because she doesn't know "what’s going to be in it."