If you’re a fan of The Big Bang Theory, you’re no doubt familiar with the method employed by other characters to soothe uptight scientist Sheldon when he gets upset: a lullaby about a soft, nice kitty that helps him settle down to sleep when he’s having trouble. That “Soft Kitty” song has also turned into big merchandising bucks, money the show doesn’t deserve according to a new lawsuit that claims the lyrics are a ripoff.

The family of a late New Hampshire nursery school teacher named Edith Newlin, who passed away in 2004, filed a federal complaint [PDF] claiming that the “Soft Kitty” song that’s proven so popular for CBS’ show about wacky scientists and their neighbor who works at a Cheesecake Factory was taken without credit from a poem she wrote in 1933 called “Warm Kitty.”

Newlin’s daughter said she had never watched the show and didn’t know about it using “Soft Kitty” until she was researching an article about her mother in August 2014. She and her sister say there’s only a “minor change in word order” between the song that’s performed on the show and their mother’s original poem, which goes: “Warm kitty, soft kitty / Little ball of fur / Sleepy kitty, happy kitty / Purr! Purr! Purr!”

In comparison, the song sung on Big Bang Theory goes, “Soft kitty, warm kitty/ Little ball of fur/ Happy kitty, sleepy kitty/ Purr purr purr.”

Willis Music published the poem in a collection called “Songs for the Nursery School,” whose registration was last renewed in 1964, according to the lawsuit. The show runners worked out a deal with Willis Music for that song privately, the lawsuit claims, but never asked Newlin’s heirs for permission. Even worse, the sitcom cites co-producer and Chuck Lorre Productions principal Bill Prady with the lyrics for the song, the complaint says.

Besides just appearing on a TV show, the lawsuit says, the song has raked in merchandising money that takes the ripoff to another level.

“The Soft Kitty lyrics have been displayed in their entirety on t-shirts, sweatshirts, hoodies, pajamas, mouse pads, mobile phone covers, wallets, air fresheners, refrigerator magnets, singing plush toys, and other products,” the complaint states. “With the exception of the singing plush toys, these merchandise items display the complete and verbatim Soft Kitty lyrics without any musical accompaniment.”

To that end, watching a clip of “Soft Kitty” on the official YouTube page for the show, multiple ads pop up on the video with links to “Soft Kitty tees” and a “Soft Kitty hoodie.”

The daughters are seeking damages and an injunction for copyright infringement.

Check out the song as seen on Big Bang Theory below:

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.