Sen. Marco Rubio, R-Fla. (Photo: AP)

Republican Senator Marco Rubio said he intends to vote against Republican tax legislation as written unless the refundable portion of the child tax credit rises from $1,100, throwing a wrench into conference negotiations.

“I want to see the refundable portion of the child tax credit increased,” the Florida Republican said Thursday. “If it stays at $1,100 I’m a no.”

Rubio and Senator Mike Lee, a Utah Republican, have proposed expanding the credit to make more of it refundable against payroll taxes, a change that would help more working class families.

Republicans have a narrow majority in the Senate, where they passed an initial version of tax legislation with just 51 votes. Losing Rubio’s support would still allow them to pass the final legislation, but would mean that Senate leaders could lose no others.

Earlier this month, senators rejected the Rubio-Lee proposal — which would have been paid for by setting a slightly higher corporate tax rate. This week, as it became clear that lawmakers were instead considering increasing the corporate rate anyway — while cutting the top individual income tax rate to 37 percent — Rubio didn’t hide his displeasure.

On Thursday, he said GOP leaders “found the money to lower the top rate” but “can’t find a little bit” more to help parents raising children.

Senate leaders have said they feel confident they have the votes to approve the bill next week. But Rubio said he has not yet received any assurances on his demand.

The Senate bill would expand the credit to $2,000 per child. Asked if it’d be tough to vote no if he’s the deciding vote, Rubio said, “Not tough at all.”

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