Pretty Maw, a rapper/songwriter, claims in a new lawsuit obtained by TMZ ... Tyga stole portions of her song, "17th," and used them without paying up.

P.M. claims she and Tyga had a deal in which he would pay her "a fixed monetary amount" for his use of her song, along with royalties from "Swap Meet," which was released in Sept. 2018. His song has more than 7 million views on YouTube.

She says not only that, Tyga induced her into allowing him to use her image and likeness for his song. She actually appears at the end of the music vid, as well.

Pretty Maw does not list the similarities between her song and his, but says "Swap Meet heavily samples" her work.

She's asking for money and an order stopping Tyga from ripping her off. We've reached out to Tyga ... so far no word back.

Getting sued is nothing new for the rapper -- he had a few lawsuits to deal with last year ... including one for allegedly bailing on a gig in Dubai, and another for allegedly not paying rent.

He also filed a $10 mil suit of his own.

Just wait 'til Soulja Boy hears about this one.