“Word for word, the short, simple lyrics of ‘We Shall Overcome’ might be some of the most influential words in the English language,” the Library of Congress writes. “It was the most powerful song of the 20th century. It started out in church pews and picket lines, inspired one of the greatest freedom movements in U.S. history, and went on to topple governments and bring about reform all over the world.”

Just a few months after a federal judge ruled that the song “Happy Birthday to You” should belong in the public domain, the victorious lawyers behind the case are now training their sights on the Civil Rights Movement’s anthem, “We Shall Overcome.”

This week, a nonprofit group called the We Shall Overcome Foundation sued Ludlow Music Inc. and The Richmond Organization, two publishers who own the copyright to the famous tune. The group, which works with orphans and the poor, was founded by a group of filmmakers who are looking to make a documentary about the song, but were denied the licensing rights for undisclosed reasons, Joe Mullin reports for Ars Technica.

While “We Shall Overcome” became an iconic symbol of the Civil Rights Movement of the 1960s, it has deep roots in American spiritual and protest music. According to the plaintiffs, it was derived from African-American spirituals, but the first printed record of the song (then called “We Will Overcome”) was in a 1909 edition of The United Mine Workers Journal, Ben Sisario reports for the New York Times. By the 1940s, it had become a classic protest song that was popularized by folk singer Pete Seeger. But in 1960, Ludlow Music Inc. and The Richmond Organization copyrighted the song and have been the arbiters of who gets to use it on screen ever since. The filmmakers are arguing that a copyright to the song should never have been granted in the first place.

"This was never copyrightable to begin with," Mark Rifkin, the lead attorney for the plaintiff, tells Joseph Ax for Reuters. "The song had been in the public domain for many, many years before anyone tried to copyright it."

According to the lawsuit, the filmmakers reached out to the publishers to obtain a license to use the song in their documentary, but were rejected.

"WE SHALL OVERCOME is a difficult song to clear," the publisher’s representative told the group, as Mullin reports. "I have been advised by our historians that we will need to review the recording that is intended to be used. The song cannot be cleared without reviewing what’s being sung and the quality of the representation of the song."

The filmmakers hired a singer to record a sample of the song, which they submitted for review. However, the publisher denied them the license and refused to explain why after multiple requests, the lawsuit says. A representative of the publisher declined to comment when Ax asked about the lawsuit.

Now, the filmmakers are looking to form a class-action lawsuit with the hopes of returning “We Shall Overcome” to the public domain, as well as compelling the music company to return licensing fees paid for the song’s use in the past.