Louisiana has become the first US state to order that every public school classroom up to university level must display a poster of the Ten Commandments.

The Republican-backed measure signed into law by Governor Jeff Landry on Wednesday describes the commandments as “the foundational documents of our state and national government”.

The law is expected to be challenged by civil rights groups, which argue that it contravenes the separation between church and state enshrined in the first amendment to the US Constitution, the so-called Establishment Clause.