The Kentucky Supreme Court dealt a major blow to school choice advocates on Thursday, declaring a controversial law that permitted people to receive tax credits for donations supporting private school tuition unconstitutional. 

The high court unanimously ruled that the state's Education Opportunity Account Program was illegal under provisions of the state constitution that require tax dollars to support "common schools." Opponents of the law said it would have diverted state funds away from public schools.

"We are compelled to agree that the EOA Act violates the plain language of Section 184," Deputy Chief Justice Lisabeth T. Hughes wrote for the court. "Simply stated, it puts the Commonwealth in the business of raising 'sum(s) … for education other than in common schools.'"

The ruling upheld a lower court decision that barred the state Department of Revenue from administering the program more than a year ago. The court's decision was welcomed by teachers' unions, who hailed it as a victory for public school education. 

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Kentucky Supreme Court Justice Lisabeth Hughes

Kentucky Supreme Court Justice Lisabeth Hughes (AP Photo/Timothy D. Easley, File)

"We simply can’t afford to support two different education systems — one private and one public — on the taxpayers’ dime, and this ruling supports that concern," said Eddie Campbell, president of the Kentucky Education Association, which represents tens of thousands of public educators. "This decision is proof that the courts continue to serve as an important check against legislative overreach."

School choice proponents harshly criticized the ruling, calling it "outside of the mainstream of legal jurisprudence."

"Today, the Kentucky Supreme Court issued a decision that will hold back thousands of Kentucky students from reaching their full potential," EdChoice Kentucky President Andrew Vandiver said in a statement.

"This effort to empower parents is too important to stop, and we will continue working to give every Kentucky student access to an education as unique as they are," he added.

The Bluegrass Institute for Public Policy Solutions, a Kentucky-based, free market think tank, accused the court of "siding with opponents of educational liberty."

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Kentucky Gov. Andy Beshear

Kentucky Gov. Andy Beshear (AP Photo/Timothy D. Easley, File)

The controversial school choice law narrowly passed Kentucky's Republican-dominated legislature, overcoming a veto from Democratic Gov. Andy Beshear.

The legal challenge focused on a key part of the law creating a form of scholarship tax credits — referred to as education opportunity accounts. The lawsuit called it a "diversion of public revenues to private schools" and asked that it be struck down.

Under the measure, private donors backing the accounts would have been eligible for tax credits from the state. The grants could have been used for an array of educational expenses, including private school tuition in several of the state’s most populated counties.

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Opponents warned the tax credits would cost the state treasury up to $25 million a year — money they said could go for public education.

Supporters said the measure offered opportunities for parents who want new schooling options for their children but are unable to afford them.

The Associated Press contributed to this report.