'Shameless' Star Steve Howey and Wife Sued By Former Nanny

"Shameless" star Steve Howey and his wife, Sarah Shahi, put their former nanny through the wringer -- over being Muslim, over her body, and sexually harassed her ... according to the nanny's lawsuit.

Howey and Shahi -- who's starred in "Person of Interest," "Chicago Fire" and "The L Word" -- hired Sarah Alaseri in July 2012 to take care of their 3 kids ... but Alaseri says Howey would berate her about following Muslim customs in their presence. She says the verbal abuse got so bad, she felt she couldn't do her daily prayers in the house.

Howey's wife, on the other hand, was all about sharing sexual gossip and innuendo with her nanny ... according to the suit. Alaseri says Shahi would encourage her to get in shape and "run off" with Howey. Why?

According to Alaseri, Shahi told her about an affair with an "A-list" actor who left her "sore" -- and she even played show and tell. The nanny says Shahi whipped out pics of her lover's junk, and said she wanted to "move on with her life" ... without Howey.

The nanny says after 3 years, the abuse was too much to handle, and she quit. She's suing for damages for back wages, harassment, wrongful termination -- basically, a lot of money.

The lawsuit is damn near ripped from a "Shameless" script. On the show, Howey's character and his wife both slept with their nanny and then invited her into a sort of 3-way marriage.

We've reached out to Howey and Shahi's reps ... no word back.

Not relevant to the suit, but still a fun fact -- Shahi is a former Dallas Cowboys cheerleader.