Lady Gaga's lawyer said that an agreement at the heart of the legal battle was "unlawful".
Song writer and music producer Rob Fusari claims that he and the Grammy Award-winning performer formed a business partnership, in which he was entitled to 20 per cent of the business.
He is claiming $30.5 million (£20.3 million) from the singer.
The lawsuit said they co-wrote songs such as "Paparazzi" and "Beautiful, Dirty, Rich."
Mr Fusari also said he came up with the 23-year-old's stage name and helped get her record deal.
He said his protégé and former girlfriend, whose real name is Stefani Germanotta, abandoned him and their partnership Team Love LLC as her career soared.
Mr Fusari claims that their business partnership entitles him to 20 per cent of her record deal.
He acknowledges that he has received $611,000 from her but says it is not his full share.
But Lady Gaga's lawyer Charles Ortner told that court that the agreement between the singer and the producer was "unlawful".
He said that Mr Fusari and his company violated statutes that prohibited them from "acting as employment agents without a license and charging Lady Gaga an unlawful fee for their purported services."
Mr Fusari's lawyer, Robert S. Meloni, called the claim "ludicrous".
"Fusari is a PARTNER in the Team Love LLC with Gag," Mr Meloni wrote.
"Rob was no more of an 'agent' for her than she is a Roman Catholic nun."
Lady Gaga won two Grammys in January: best dance recording, for "Poker Face," and best electronic or dance album for "The Fame."
A spokesman for Lady Gaga, who is on tour in Australia, declined to comment on the suit.
