Oklahoma will require schools to teach the Bible and have a copy in every classroom, the state’s top education official announced Thursday.

Effective immediately, Oklahoma schools are required to incorporate the Bible as part of the curricula in grades five through 12, according to a memo Superintendent of Public Instruction Ryan Walters sent to all school districts. Schools are instructed to refer to the Bible and the Ten Commandments for their “substantial influence on our nation’s founders and the foundational principles of our Constitution.”

“Immediate and strict compliance is expected,” the memo noted.

Walters said at a state Board of Education meeting Thursday, “We’ll be teaching from the Bible in the classroom to ensure that this historical understanding is there for every student in the state of Oklahoma.”

Americans United for Separation of Church and State, a nonprofit civil liberties group, said in a statement that Walters’ new Bible policy is “trampling the religious freedom of public school children and their families.”

“This is textbook Christian Nationalism: Walters is abusing the power of his public office to impose his religious beliefs on everyone else’s children,” Rachel Laser, the group’s CEO, said in the statement. Her organization is “ready to step in,” she wrote, though she stopped short of vowing legal action. The group has already sued to block a new Louisiana law requiring the Ten Commandments to be displayed in public schools.

Walters, a former high school history teacher, has built a national profile over his first year and a half in office as a staunch proponent of incorporating Christian beliefs and teachings into state education policy.

Gov. Kevin Stitt, a Republican, recently approved a package of regulations put forward by Walters that included time for prayer in schools and expanded the state Education Department’s “foundational values” to acknowledge a “Creator” and the existence of good and evil.

But Walters has also drawn pushback. Stitt issued an executive order this month prohibiting state agencies from entering into sole-source contracts with marketing and public relations firms after Walters hired a public relations firm at $200 per hour to help him get national media attention.

The state Supreme Court ruled this week that a state contract to fund a Catholic charter school violated both state and federal law and must be voided. It would have been the country’s first religious charter school.

Walters called the ruling “sanctioned discrimination against Christians” in a statement. “This ruling cannot and must not stand,” he wrote.

State Attorney General Gentner Drummond, also a conservative Republican, disagreed.

“This decision is a tremendous victory for religious liberty,” he said in a statement. “The framers of the U.S. Constitution and those who drafted Oklahoma’s Constitution clearly understood how best to protect religious freedom: by preventing the State from sponsoring any religion at all.”

This article was originally published on NBCNews.com