LINCOLN, Neb. (AP) — The American Civil Liberties Union of Nebraska is warning a local school district about a “loyalty oath” to the United States that employees are required to sign.

The ACLU sent the letter to Hastings Public Schools on Friday after receiving complaints from employees.

The group says the pledge requirement came from a 1951 state law, and even though it’s still on the books, the U.S. Supreme Court has ruled that employees cannot be required to sign such a pledge. ACLU of Nebraska legal director Amy Miller says attempting to enforce the law will expose the district to a civil rights lawsuit.

Hastings Schools Superintendent Craig Kautz says the district’s attorney advised him that there are two oath requirements in state law, and one is still legally valid.