Trey Songz has been sued for sexual assault ... after exposing a woman's breast at a pool party outside a Connecticut casino.
According to TMZ, legal documents indicate that the woman -- who's suing anonymously as a Jane Doe -- is coming after Trey, his production company, record exec Kevin Liles, and Atlantic Records over the 2013 incident.
The woman fired off a demand letter to Trey last year, claiming the rapper pulled her breast out of her bikini top without consent, exposing her to the crowd at his "Foxwoods Liquid Sundays with Trey Songz" event ... providing video of the ordeal.
The docs say the multiple defendants should have known about his "sexual proclivities" and are therefore responsible for failing to keep Trey under control during the event.
The woman's attorneys claim she was humiliated and left with long-lasting emotional distress ... adding their client could not stop thinking about it and eventually left her promising career a few months later due to the embarrassment.
In last year's letter, her lawyers claimed his 2021 Vegas sexual assault case -- which was dropped weeks before the demand letter was sent -- triggered Megan to seek justice.
She gave Trey and Co. weeks to respond before moving forward with legal action ... and now she's seeking at least $10 million in damages.
We reached out to Trey's rep ... so far, no word back.
Trey's attorney, Michael Freedman, says; "This is yet another example of decade-old allegations being repurposed into a federal case to take advantage of California’s constitutionally questionable new lookback window. We look forward to vindicating Trey on the merits in court."