For her cover shoot on the current issue of PEOPLE, Jessica Simpson is sporting a light gold, strapless Oscar de la Renta gown. But in her video for "With You," the "Newlyweds" star agreed to sport a T-shirt bearing the logo of the automotive racing company Motorock -- and now she's suing, claiming she never got paid for the endorsement.

The 23-year-old pop star and her father, Joe Simpson, have filed a breach-of-contract lawsuit against the New Jersey-based production company 4 Dog Productions, seeking $140,000 in damages, the Smoking Gun Web site reports. They claim the company has reneged on its agreement to pay Simpson for plugging the T-shirt in her video.

The legal papers, dated March 26, were submitted to New York's Federal District Court by the Simpsons' Manhattan-based law firm.

They also claim that, as part of a six-figure promotion deal last year, Jessica would also do some related promotional appearances, including a one-hour performance at last October's Grand Prix of Puerto Rico -- which 4 Dog canceled without Simpson's consent, according to the papers.

Mike Zaccaro, owner of 4 Dog Productions, declined comment to Smoking Gun, saying that he had yet to see the legal papers.