The "Modern Family" star is being sued by Richard Konigsberg, who claims he served as her personal and professional manager for 15 years and helped her land her breakthrough role on the hit sitcom.

In the lawsuit, obtained by TMZ, Richard says Sarah unceremoniously fired him in April in what he believes is an attempt to get out of paying him his 10% commission on a couple lucrative projects he helped Sarah land.

For starters, Richard says he had a longstanding agreement where Sarah would pay him 10% of all the money she made during his time as her manager ... and he says she was paying him 10% of her "Modern Family" royalties until she fired him.

Richard says when he got axed, Sarah told him he would no longer be paid commission for 'MF' and would only get 10% of what she made for a theater production of '"Little Shop of Horrors."

Richard is going after Sarah for damages ... and he wants a declaration from the court that Sarah is obligated to pay him 10% on all the money she makes from projects she landed during his tenure as her manager.