The Oklahoma state superintendent ordered all public schools to teach the Bible effective immediately, arguing it's a "necessary historical document," in a controversial move that is expected to be swiftly challenged.

In his announcement Thursday, Superintendent Ryan Walters, a Republican, said the Bible is "a necessary historical document to teach our kids about the history of this country, to have a complete understanding of Western civilization, to have an understanding of the basis of our legal system," according to The New York Times.

Students in grades 5 through 12 will be subject to the religious lessons and all instructors have been directed to teach from the Bible, said Walters, CNN reported.

Walters said "immediate and strict compliance" is expected, according to the Associated Press.

Americans United for Separation of Church and State President Rachel Laser said the group was prepared to "step in and protect all Oklahoma public school children and their families from constitutional violations of their religious freedom," the Times reported.

"Public schools are not Sunday schools," she continued, noting "public schools may teach about religion, but they may not preach any religion."

The new directive comes days after Republican Gov. Jeff Landry ordered every public school classroom in Louisiana to display the Ten Commandments starting in January.