WASHINGTON >> The Republicans’ razor-thin margin for driving their sweeping tax package through the Senate has been jeopardized by Florida’s Marco Rubio, who says he will vote against it unless negotiators expand the tax credit that low-income Americans can claim for their children.

Rubio’s potential defection complicates Republican leaders’ goal of muscling the $1.5 trillion bill through Congress next week.

Senate Republicans could still pass the package without Rubio’s vote, but they would be cutting it extremely close. An original version was approved by only 51-49 — with Rubio’s support.

The co-sponsor of Rubio’s proposed change, Republican Sen. Mike Lee of Utah, is undecided on the overall bill and pushing to make the credit as generous as possible.