For decades, characters on screens big and small have been held back from singing “Happy Birthday” to one another by copyright law.

Yes, if producers want to hear the song in their final cut, they need to pay a sum to Warner/Chappell, the publishing division of Warner Music Group, which ended up as keeper of the song after a series of acquisitions stretching back to the 1930s.

But soon that could all change. In 2013, documentarian Jennifer Nelson sued Warner/Chappell with the goal of making “Happy Birthday” public property, and now her team has found some compelling new evidence to rebuff a key argument made by lawyers for the music behemoth.

Warner/Chappell’s case, according to The Hollywood Reporter, rests on the idea that the song could only be freed from copyright claims if the sisters credited with writing it had allowed it to be published — sans copyright notice — before it was registered with the copyright office in 1935. Nelson’s lawyers have done just that, unearthing a 1922 copy of “The Everyday Song Book,” containing lyrics to “Happy Birthday.”

A quick history: The sisters, Mildred and Patty Hill, wrote a tune called “Good Morning To You” in the late 1800s. When the lyrics eventually shifted to celebrate birthdays, we were left with the song practically everyone in the English-speaking world knows to use to embarrass their friends at restaurants.

If Nelson wins the case, Warner/Chappell would also be asked to return millions of “Happy Birthday” royalty fees collected over the past four years. That includes payouts to studios big and small, like Nelson’s Good Morning To You Productions. As it stands, the current copyright wouldn’t expire until 2030.

A hearing scheduled in Los Angeles today could determine the song’s fate. Of course, it’ll always be legal to serenade family and friends off-camera as they turn one year older.

But we would very much like to live in a world where we can watch actors singing “Happy Birthday” freely on screen whenever a show’s writers feel like making it happen.

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