Story highlights Republicans have a slim majority in the Senate to pass their tax legislation

The GOP can only lose two votes in the chamber

(CNN) Sen. Marco Rubio, a Republican from Florida, told congressional leadership that he will not support the latest version of the GOP tax bill if the legislation doesn't make the child tax credit more generous.

"I've been pretty consistent in my communications on this issue and that is I want us to see the refundable portion of the child tax credit increased from its current number," Rubio told reporters on Capitol Hill on Thursday. "If it stays at $1,100, I'm a 'no.' Let's hope it doesn't."

First reported by The Washington Post on Thursday, Rubio is a potential problem as the Senate GOP prepares to bring a tax bill to the floor for a vote next week.

Republican leaders are working with an already thin majority in the Senate. Majority Leader Mitch McConnell can only afford to lose two votes and already Sen. Bob Corker, a Republican from Tennessee, voted against the last version of the bill. Corker said Wednesday he still maintained many of the same concerns from his last vote with the most recent version of the bill.

"Senator Rubio has consistently communicated to the Senate tax negotiators that his vote on final passage would depend on whether the refundability of the Child Tax Credit was increased in a meaningful way," Olivia Perez-Cubas, an aide to Rubio, told CNN in a statement Thursday.

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