Rupa Marya v. Warner Chappell Music was fought over the copyright status1 of the song “Happy Birthday to You”. A key factor in the order for summary judgement came in this all-time great quote:

Obviously, pianos do not sing.

Judge George H King
Rupa Marya v. Warner Chappell Music

At the time of lawsuit, Warner was collecting royalties — around $2 million a year — for “Happy Birthday to You” despite the fact that the melody was in the American public domain. They claimed that the lyrics were still under copyright and that they owned the rights to them.

Although Warner had acquired some “Happy Birthday”-related rights, it wasn’t clear what those rights covered since the original transfer agreements had been lost. The judge ruled that the secondary sources did not support Warner’s claim on the lyrics specifically, assuming they were still under copyright at all. Settlement terms following the summary judgement definitively assigned the song to the American public domain.

As far as I can tell, the European copyright to both the “Happy Birthday” lyrics and melody would have been still valid, albeit with disputed ownership, until it expired in 2017.