OKLAHOMA CITY — A state school board at Oklahoma voted Monday to approve what would be the first publicly funded religious school in the nation, despite a warning from the state’s attorney general that the decision was unconstitutional.

The Statewide Virtual Charter School Board voted 3-2 to approve the application by the Catholic Archdiocese of Oklahoma to establish the St. Isidore of Seville Virtual Charter School. The online public charter school would be open to students across the state in kindergarten through grade 12.

Oklahoma’s attorney general, Gentner Drummond, had warned the board that such a decision clearly violated the Oklahoma Constitution.

“The approval of any publicly funded religious school is contrary to Oklahoma law and not in the best interest of taxpayers,” Mr. Drummond said in a statement shortly after the board’s vote. 

“It’s extremely disappointing that board members violated their oath in order to fund religious schools with our tax dollars. In doing so, these members have exposed themselves and the state to potential legal action that could be costly.”

The Archdiocese of Oklahoma said in the “vision and purpose of the organization” section of its application that: “The Catholic school participates in the evangelizing mission of the Church and is the privileged environment in which Christian education is carried out.”

“We are elated that the board agreed with our argument and application for the nation’s first religious charter school,” the executive director of the Catholic Conference of Oklahoma, Brett Farley, said.

Americans United for Separation of Church and State denounced the board’s approval.

“It’s hard to think of a clearer violation of the religious freedom of Oklahoma taxpayers and public-school families than the state establishing the nation’s first religious public charter school,” the group’s president and chief executive, Rachel Laser, said in a statement. 

“This is a sea change for American democracy. Americans United will work with our Oklahoma and national partners to take all possible legal action to fight this decision and defend the separation of church and state that’s promised in both the Oklahoma and U.S. Constitutions.”

Oklahoma’s Republican governor, Kevin Stitt, who earlier this year signed a bill that would give parents in the state a tax incentive to send their children to private schools, including religious schools, praised the board’s vote.

“This is a win for religious liberty and education freedom in our great state, and I am encouraged by these efforts to give parents more options when it comes to their child’s education,” Mr. Stitt said in a statement.