"Happy Birthday to You" is the subject of a fresh US legal dispute, with a production firm claiming the tune's copyright owner has no exclusive right to the most popular song in the English language.

Good Morning to You Productions (GMTY) has filed suit in a federal court in New York against Warner/Chappell Music demanding that the government declare invalid its copyright over the song, saying it belongs in the public domain.

The lawsuit also demands the return of "millions of dollars of unlawful licensing fees collected by defendant Warner/Chappell pursuant to its wrongful assertion of copyright ownership of the song," the 26-page suit says.

The production company, which is making a documentary on the tune, said it was forced to pay $1,500 to use the song in order to avoid being fined $150,000 for unauthorized use.

"Warner/Chappell's demand was coercive in nature, and GMTY's entering into the license agreement and payment of $1,500 was involuntary," it said.

A spokesman for Warner/Chappell declined to comment on the suit.

According to GMTY, the tune comes from a song called "Good Morning to All," which was composed in 1893 by sisters Mildred and Patty Hill, who sold the rights to Clayton F. Summy.

The song in its present form was released in 1924 by Robert Coleman, setting off a series of legal disputes.

"Irrefutable documentary evidence, some dating back to 1893, shows that the copyright to 'Happy Birthday to You,' if there ever was a valid copyright to any part of the song, expired no later than 1921," when Summy failed to renew it, the GMTY lawsuit says.

"If defendant Warner/Chappell owns any rights to Happy Birthday to You, those rights are limited to the extremely narrow right to reproduce and distribute a specific piano arrangement for the song published in 1935."

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