For The Big Bang Theory fans, "Soft Kitty" has become a standard in the longtime running CBS sitcom and is the tune that everyone sings to put their own "Sheldon" to sleep. However, one family isn't too pleased with the song's popularity, especially because they believe the show's producers stole it from their mom.

Ellen Newlin Chase and Margaret Chase have filed a "copyright infringement action" against CBS, its numerous media partners and the show's producers for using the song that their late mother Edith Newlin, a former New Hampshire teacher, wrote in the 1930s. The family seeks "unspecified damages" and claim that the song was used eight times in March 2008 and has been used in various kinds of merchandise for the show.

"The Soft Kitty Lyrics are among the best-known and most popular aspects of The Big Bang Theory," the lawsuit states. "They have become a signature and emblematic feature of the show and a central part of the show's promotion."

The lawsuit also claims that the lyrics were published in 1937 by the Willis Music Company as part of the book, Songs for the Nursery School, and that Willis and Warner Bros. Entertainment Inc. and one of the Big Bang producers struck a deal for the song even though no one could "lawfully secure rights."

Listen to the song below.