V. Stiviano -- Investigated for Allegedly Extorting Donald Sterling Over Recordings

V. Stiviano is under criminal investigation for allegedly extorting Donald Sterling by demanding money in return for keeping more audio recordings secret ... TMZ Sports has learned.

Law enforcement sources tell TMZ ... a senior investigator for the L.A. County D.A.'s Bureau of Investigation contacted Shelly Sterling Tuesday ... asking for an interview in connection with the extortion investigation.

Donald Sterling gave an interview last week ... telling a magazine, "I wish I had just paid her off."

TMZ Sports first reported ... Stiviano claims to have 100 plus hours of recordings of conversations between her and Sterling.

Stiviano's people told us a week ago ... Sterling called her after we posted the audio ... asking her, "How can we make this go away?" We have since learned it was NOT Sterling who initiated the call -- it was Stiviano.

And we've learned the investigation is also focusing on whether Stiviano illegally recorded Sterling ... recording private conversations without the consent of all parties is a crime in California.