WASHINGTON (AP) - Republican Sen. Marco Rubio will vote for his party's $1.5 trillion tax bill. That gives a major boost to the prospects that GOP leaders will be able to push their prized measure through Congress next week.

The Florida lawmaker had said he'd oppose the legislation unless his colleagues made the per child tax credit more generous for low-income families.

On Friday, Republicans said the final legislation would do just that. Lawmakers said the bill would now let low-earners using the credit get up to $1,400 in IRS refunds if they owe little or no taxes. That's up from $1,100 in the earlier version.

Rubio tweeted that the change is "a solid step toward broader reforms which are both Pro-Growth and Pro-Worker."

Rubio spokeswoman Olivia Perez-Cubas said that meant he'd vote yes.

Ailing Republican Senators John McCain and Thad Cochran will be able to cast their votes for the GOP tax package next week.

That's the word from fellow GOP Sen. Rob Portman of Ohio. He told reporters on Friday: "All of our thoughts and prayers go out to Sen. McCain. He's having a tough time. I am told he will be here next week and voting. And more importantly we all wish him the best of health."

McCain, 81, is hospitalized at Walter Reed Medical Center where the Arizona senator is being treated for the side effects of brain cancer treatment.

Thad Cochran, 80, of Mississippi had a non-melanoma lesion removed from his nose earlier this week.

Portman said: "I'm told he will be here next week also."

Several Republican senators are optimistic about passage of the far-reaching GOP tax package next week.

Ohio Sen. Rob Portman, one of the House-Senate negotiators, said Friday he believes they have the votes to pass the bill. His comments came as fellow Republican, Florida Sen. Marco Rubio, pressed for expansion of the child tax credit, saying he's a "no" vote if it's not a significant boost.

Pennsylvania Sen. Pat Toomey told reporters: "All I'm going to say is I'm optimistic that we have enough support to pass the bill."

Wyoming Sen. Mike Enzi said "there's a problem with every single senator until the last vote is cast." He added: "There are changes in this bill that I think can form some of the things he (Rubio) asked for."

Republican Congresswoman Kristi Noem says the child tax credit has been expanded for low-income families in an effort to win Sen. Marco Rubio's support for a sweeping tax package.

The tax package would double the per-child tax credit from $1,000 to $2,000. The bill originally made a portion of the credit - $1,100 - available to families even if they owe no income tax. Noem says that amount has been increased to $1,400. Rubio said he wanted the $1,100 figure increased, but he did not say by how much.

Low-income taxpayers would receive the money in the form of a tax refund, which is why it's called a "refundable" tax credit.

Noem, of South Dakota, said the change should win Rubio's support but she had not heard directly from him.

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