Republican Maine Sen. Susan Collins said Monday afternoon that she will vote for the final version of the Republican tax bill, likely guaranteeing that it will pass the upper chamber this week.

"I will cast my vote in support of the conference agreement on the Tax Cuts and Jobs Act," Collins said in a speech on the Senate floor. "While it is by no means perfect, on balance this reform bill will provide much-needed tax relief."

Collins, a centrist, was regarded as one of the Republicans most likely not to support the bill. With her support, it is expected to reach the 50 "yes" votes needed for passage.

"Tax relief and reform will lift our economy, leading to higher wages for workers and more revenue for government," she said.

Collins voted for the Senate version of the bill, after Senate Majority Leader Mitch McConnell and President Trump promised her that two measures to stabilize Obamacare would be passed by the end of the year. She said she wanted to review the joint House-Senate agreement before stating that she would vote for the version that would go to President Trump's desk. In Monday's speech, she touted three amendments of hers that were included in the bill.

Likewise, Sen. Mike Lee, R-Utah, tweeted Monday afternoon that he will "proudly vote for" the bill, now that he has finished reading it.

Republicans have 52 members in the Senate, meaning they can lose two votes and still pass the tax bill without Democrats.

They are down one vote, as Sen. John McCain, who has an aggressive form of brain cancer, is recuperating in Arizona for the month.

Yet none of the other 51 Republicans have said that they will vote against the measure, and now several undecideds have announced their support for it. Tennessee Sen. Bob Corker, the only Republican to vote against the Senate version of the bill, said last week he would support it.