Sens. Mike Lee and Susan Collins will support the Republican tax plan, they said Monday, solidifying Republican hopes to pass a bill to overhaul the American tax code this week.

The commitments from Lee and Collins — of Utah and Maine, respectively — leave only one GOP senator publicly undeclared on the bill: Jeff Flake of Arizona. With Sen. John McCain fighting brain cancer in his home state of Arizona, the bill will fail in the Senate if two of the remaining 51 Republicans oppose it.

In a tweet, Lee said he will "proudly vote" for the plan after reading the legislation. He said it "will cut taxes for working Utah families."

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Lee and Sen. Marco Rubio, R-Fla., pushed Republican leaders to expand the child tax credit in the final version of the legislation. On Friday, Rubio said he would vote for the bill after the GOP increased the refundable portion of the credit.

The child tax credit would double to $2,000 per child under the plan, with $1,400 of that refundable.

GOP Sen. Bob Corker of Tennessee — the only Republican to vote against the Senate's version of the bill — also committed Friday to backing the final plan.

The House plans to vote on the joint legislation on Tuesday. The Senate will move to approve it and send it to President Donald Trump's desk before Thursday.