Nine Louisiana families have sued the state over a new law that orders every public school classroom to display a poster of the Ten Commandments.

The suit, filed in federal court on Monday, comes less than a week after Governor Jeff Landry ratified the Republican-backed measure.

It is expected to kick off a drawn-out legal battle that could reach the US Supreme Court.

The law is the first of its kind in the US, and governs all classrooms up to and including university.

Under the legislation, HB71, every classroom that receives state funding must by 2025 prominently display the biblical text in a "large, easily readable font" on a poster that is 11 inches by 14 inches (28cm by 35.5cm).

The commandments must be "the central focus" of the display, the law says.

The complaint, backed by civil rights groups, claims that such a display violates the First Amendment of the US Constitution, which guarantees freedom of religion, and that the display "pressures" students into adopting the state's favoured religion.

The law "simply cannot be reconciled with the fundamental religious freedom principles that animated the founding of our nation", wrote the plaintiffs, who include both rabbis and pastors.

“It sends the harmful and religiously divisive message that students who do not subscribe to the Ten Commandments do not belong to their own school community."

The court filing also claims that a central premise of the new law - that the Ten Commandments have long been linked to public education in the US - is partially based on a misquote.

In the law, Louisiana legislators quote the fourth president, James Madison, as saying: “We have staked the whole future of our new nation … upon the capacity of each of ourselves to govern ourselves according to the moral principles of the 10 Commandments.”

According to the suit, "that quotation is fabricated".

Governor Landry's office did not respond to a request for comment.

A representative for the bill's Republican author, Dodie Horton, declined to comment.

Ms Horton has previously spoken of the importance of returning a "moral code" to classrooms. She was quoted saying "it’s like hope is in the air everywhere" as the bill was rubber-stamped by the governor.

There have previously been numerous legal battles over the display of the Ten Commandments in public buildings, including in courts, police stations and schools.

In 1980, in the case Stone v Graham, the Supreme Court struck down a similar Kentucky law requiring that the document be displayed in elementary and high schools. This precedent has been cited by the groups contesting the Louisiana law.

In its ruling, the Supreme Court said the requirement "had no secular legislative purpose" and was "plainly religious in nature" - noting that the commandments made references to worshipping God. (BBC)

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