Chris Brown -- Model Claims His Company Screwed Her Royally

Chris Brown's modeling agency is accused of dirty dealing by a model who claims they're using her image without paying her a dime.

Stasiya Maria claims she was invited to a test shoot for Legendary Faces on March 21 that turned into a giant casting call. She says she had no idea what was going on, but played along ... posing for a few pics with other girls.

Maria claims she never signed a release and is furious she's now featured in two Instagram promotional videos the company produced.

Maria's lawyer fired off a letter to the company, demanding it take the videos down ... or she'll sue.