Lady Gaga sued her former music producer Rob Fusari saying he shouldn't get any share of fees he says he's entitled to after claiming he discovered her, dated her and helped develop her sound and style.

The singer sued Fusari and his business the day after he sued her production company, claiming she breached a contract that entitled him to 20 per cent of some of her earnings.

Fusari alleges in his complaint that he is her former boyfriend. He said he helped mentor the "young Italian girl", whose real name is Stefani Germanotta.

Gaga claims in her lawsuit that the contract "was structured in such a way to mask its true purpose — to provide the defendants unlawful compensation for their services as unlicenced employment agents".

She said the 2006 contract she signed with Fusari was "void and unenforceable" because New York and New Jersey state laws were created "to protect employees from predatory and financially abusive practices".

In his complaint, Fusari seeks more than $30 million in damages.