NEW ORLEANS — A panel of three federal appellate judges has ruled that a Louisiana law requiring the Ten Commandments to be posted in each of the state’s public school classrooms is unconstitutional.

The ruling Friday marked a major win for civil liberties groups who say the mandate violates the separation of church and state, and that the poster-sized displays would isolate students — especially those who are not Christian.

The mandate has been touted by Republicans, including President Donald Trump, and marks one of the latest pushes by conservatives to incorporate religion into classrooms. Backers of the law argue the Ten Commandments belong in classrooms because they are historical and part of the foundation of U.S. law.

The plaintiffs’ attorneys and Louisiana disagreed on whether the appeals court’s decision applied to every public school district in the state or only the districts party to the lawsuit.

“All school districts in the state are bound to comply with the U.S. Constitution,” said Liz Hayes, a spokesperson for Americans United for Separation of Church and State, which served as co-counsel for the plaintiffs.

The appeals court’s rulings “interpret the law for all of Louisiana,” Hayes added. “Thus, all school districts must abide by this decision and should not post the Ten Commandments in their classrooms.”

Louisiana Attorney General Liz Murrill said she disagreed and believed the ruling only applied to school districts in the five parishes that were party to the lawsuit and that she would seek to appeal the ruling.

The 5th U.S. Circuit Court of Appeals’ order stems from a lawsuit filed last year by parents of Louisiana school children from various religious backgrounds, who said the law violates First Amendment language guaranteeing religious liberty and forbidding government establishment of religion.

The mandate was signed into law last June by Republican Gov. Jeff Landry.

The court’s ruling backs an order issued last fall by U.S. District Judge John deGravelles, who declared the mandate unconstitutional and ordered state education officials not to take steps to enforce it and to notify all local school boards in the state of his decision.

Law experts have long said they expect the Louisiana case to make its way to the U.S. Supreme Court, testing the conservative court on the issue of religion and government.

In 1980, the U.S. Supreme Court ruled that a similar Kentucky law violated the Establishment Clause of the U.S. Constitution, which says Congress can “make no law respecting an establishment of religion.” The high court found that the law had no secular purpose but served a plainly religious purpose.

In 2005, the Supreme Court held that such displays in a pair of Kentucky courthouses violated the Constitution. At the same time, the court upheld a Ten Commandments marker on the grounds of the Texas state Capitol in Austin.