Louisiana’s highest court ruled Tuesday that Gov. Bobby Jindal’s hallmark school voucher plan violates the state’s constitution because of how it is funded.

The state Supreme Court found that the school voucher plan is illegal because it diverts tax dollars to private schools from Louisiana’s “minimum foundation program,” which was created under the state constitution to pay for public schools.

The program, which began in 2008, currently allows 4,700 students to use public funds to attend private schools and was planned to be expanded to 8,000 students by September.About 700,000 students attend public schools in Louisiana.

In the majority opinion, Justice John Weimer wrote that “the constitution prohibits those funds from being expended on the tuition costs of nonpublic schools and nonpublic entities.”

The 6 to 1 decision is a major setback for Jindal, who has promoted the voucher plan as the most expansive in the country and is considered a possible Republican presidential candidate in 2016. It comes at a time when his popularity rating in his state has plummeted.

Jindal said he would figure out another way to find $40 million in the state budget to fund the vouchers, saying that he is “committed to making sure this program continues.

“The bottom line is that our kids only get one chance to grow up and we are committed to making sure choice is alive and families can send their children to the school of their choice,” Jindal said in a statement.

In his role as chairman of the Republican Governors Association, Jindal has been nationally promoting the idea of school vouchers, charter schools and other market-based changes to public education.

Steve Monaghan, the president of the Louisiana Federation of Teachers, the lead plaintiff in the case, said the voucher program had been draining resources from public schools. He called the ruling a “breath of fresh air.”

“The constitution in this case was clearly written and the jurists did what they were supposed to do: look at it in an unbiased and non-partisan manner,” Monaghan said Tuesday from the state capitol in Baton Rouge. His union was joined in the case by the Louisiana Association of Educators and the Louisiana School Boards Association.

Jeanne Allen, president of the Center for Education Reform, a pro-voucher group, urged Jindal to appeal the decision to the U.S. Supreme Court. “The Louisiana justices’ actions today violate the civil rights of parents and children who above all are entitled to an education that our founders repeated time and time again is the key to a free, productive democracy,” Allen said.

But Francisco M. Negrón Jr., general counsel at the National Association of School Boards, said there did not appear to be grounds for a federal appeal. “The state supreme court pretty much has the final word on that, unless there is some overriding federal questions, which I just don’t see in this case,” he said.