Copyright scholars have long been pretty certain that "Happy Birthday to You" is in the public domain, despite the fact that Warner/Chappell claims copyright on it and charges impressive licensing fees to use it in public performances. Those fees, however, are much lower than a copyright lawsuit would be, so everyone shrugs and pays them. Until now.
A documentary film company working on a movie about "Happy Birthday" has assembled a huge body of evidence showing that the song has been in the public domain since the 1920s, and is suing Warner to get them to return the hundreds of millions they've improperly charged in licensing since. This is gonna be great.
The full lawsuit, embedded below, goes through a detailed history of the song and any possible copyright claims around it. It covers the basic history of "Good Morning to You," but also notes that the "happy birthday" lyrics appeared by 1901 at the latest, citing a January 1901 edition of Inland Educator and Indiana School Journal which describes children singing a song called "happy birthday to you." They also point to a 1907 book that uses a similar structure for a song called "good-bye to you" which also notes that you can sing "happy birthday to you" using the same music. In 1911, the full "lyrics" to Happy Birthday to You were published, with a notation that it's "sung to the same tune as 'Good Morning.'" There's much more in the history basically showing that the eventual copyright that Warner/Chappell holds is almost entirely unrelated to the song Happy Birthday to You.
The detail in the filing is impressive, and I can't wait to see how Warner/Chappell replies. As the filing notes, there are a variety of copyright claims around the song, but all are invalid or expired, and the very, very narrow copyright that Warner/Chappell might hold is not on the song itself. In other words, Warner/Chappell is almost certainly guilty of massive copyfraud — perhaps the most massive in history — in claiming a copyright it clearly has no right to.