Image copyright University of Louisville Image caption A portion of a music manuscript for Happy Birthday's predecessor - "Good Morning to All"

Happy Birthday To You is a staple of birthday parties around the world - but it can't be sung on TV or in movies and other public performances without paying a hefty sum. That might change soon, says journalist Natalie Villacorta.

The music to Happy Birthday To You was written in the late 19th Century by two sisters who called their version Good Morning To All. That song later evolved into the version popular today and was copyrighted by the sisters' publisher. The publisher and the rights to the song were eventually purchased by Warner/Chappell for $25m (£16m) in the 1980s.

But now a group of artists is challenging Warner/Chappell's claim to the copyright.

The challengers said in July they had found proof that the song belongs in the public domain, making it available for anyone to use, for any purpose, at no cost. They say a 1922 songbook containing the song predates the song's 1935 copyright. A ruling in the case could put the song in the public domain years before Warner/Chappell claims its copyright expires in the US, in 2030.

Image copyright University of Louisville Image caption The Hill sisters - Mildred and Patty wrote the famous celebration song

For now, people who want to use Happy Birthday To You in a movie, television episode, advertisement, or other public performance must pay Warner/Chappell a fee. The company rakes in about $2m per year from these fees, according to an estimate by George Washington University Professor Robert Brauneis, who is now working as a consultant to the plaintiffs in the case.

Warner/Chappell declined to confirm this figure or provide further comment.

One of the plaintiffs is documentary filmmaker Jennifer Nelson, who set out to make a movie about the song and ended up suing Warner/Chappell after learning she would have to cough up $1,500 to feature the song in her film.

Suing is just the most recent reaction to the song's licensing fee. In the past, advertisers, writers, and even chain restaurants have devised clever ways to skirt the copyright.

They have included just the beginning or the end of the song, played For He's A Jolly Good Fellow instead, or crafted a completely different birthday song.

Image copyright Getty Images Image caption Happy Birthday's copyright is held by a subsidiary of the music giant Warner

And over the last few years, they've developed a new tactic - joke about how they can't sing the song because the licensing fees are too expensive.

In the movies

According to the Internet Movie Database, Happy Birthday To You has been played in nearly 150 movies, but hundreds more contain birthday scenes that skip the song altogether.

Image copyright University of Louisville Image caption Remembering the Hill sisters in Louisville

Paul Greco, has been working as a music producer in the advertising industry since 1991 and now works at the agency J Walter Thompson New York. He says in all his years in the industry, he hasn't once licensed the song, nor could he think of any notable ads that had used it.

He attributes its absence to the high cost of the licence, even if the entire song isn't played.

"Once we found out that there was a copyright involved, the sort of idea would go another way because it just seemed like for advertisements it was a bit cost prohibitive to use the song," Greco explained.

Ideas involving children's birthday parties would often be tossed because of the licensing fee, Greco says, or his team would create its own music or pick a song that was in the public domain.

The song is probably heard in movies and on television more because the licensing fee is cheaper, he says, since the aim is not to help a brand sell its product.

Image copyright Getty Images

Another common place you won't hear the song is during birthday celebrations at chain restaurants. Some chains have written their own birthday songs to avoid paying licensing fees, according to Brauneis.

With the emergence of the sound chip card in the 1990s, greeting card companies also came up with creative alternatives to using Happy Birthday To You.

David Ellis Dickerson, who worked at Hallmark as a greeting card writer and editor from 1994 to 1999, said the profit margin on cards was already so small that paying the licensing fee to use the song in every single card was out of the question.

Instead they came up with their own versions.

"If you can still find those audio chip cards, see what they're playing because it's usually some really, really obvious variation, in-house variation, that sounds Happy Birthday-like but doesn't quite do it," he says.

Poking fun at the copyright

But in recent years writers have begun to make fun of the fact that they can't include the song because of the licensing fee.

"It's almost become a cliché now to make fun of the fact that we're not allowed to sing this," says Robert Thompson, director of the Bleier Center for Television and Popular Culture at Syracuse University in New York.

In a 2009 episode of the NBC sitcom 30 Rock, the show's crew throws a birthday party when the song's copyright comes up.

"Did you know that if you sing Happy Birthday on a TV show you have to pay for it?" one character asks before the cast breaks into song. They only manage to get out "Happy" before they're cut off by the entrance of another character, who spares 30 Rock from paying the fee

Image copyright Thinkstock Image caption Sing it in the privacy of your own home - for now

Last year, late night show host Stephen Colbert mocked the copyright on the 90th anniversary of the supposed publication date of the song. He wished the song a happy birthday and began to sing the familiar song when a screen popped up that said - "Sorry! Technical difficulties."

"Sorry folks, it turns out you cannot sing Happy Birthday to Happy Birthday even on Happy Birthday's happy birthday," Colbert joked, citing Warner's royalty fees.

He then offered America a "royalty-free" Happy Birthday song to the tune of the Star-Spangled Banner. "Happy birthday to you, happy birthday to me. Now we all get to sing happy birthday for free," he crooned. "Warner music can't sue me and the home of the brave."

These jokes highlight the dissonance between the song's ubiquity in American culture—its transcendence of social class, age and geography—Thompson says, and the fact that a single company holds exclusive rights to it and charges a fee for using it in public performances.

But that dissonance could be over soon - if a judge declares Warner's copyright is invalid.