A judge ruled on Tuesday that the long-claimed copyright on “Happy Birthday to You,” the most popular tune in the English language, is not valid.

The decision, by Judge George H. King of United States District Court in Los Angeles, is a blow to the music publisher Warner/Chappell and its parent company, the Warner Music Group, which have controlled the song since 1988 and reportedly still collect some $2 million annually in licensing fees for it.

If the judge’s ruling stands, “Happy Birthday to You” would become part of the public domain. “Since no one else has ever claimed to own the copyright, we believe that as a practical matter, this means the song is public property,” said Mark C. Rifkin, a lawyer for the plaintiffs.

The case, filed in 2013 by Jennifer Nelson, an independent filmmaker planning to make a documentary about the song, has been closely watched as a challenge to long copyright terms and corporate control of common culture.