Trey Songz Demand Letter from New Accuser Video of Incident Shows Him Expose Her Breast

Trey Songz has a new accuser -- a woman whose attorneys are demanding he pay for allegedly groping their client ... and they say the video makes their case a slam dunk.

The demand letter, obtained by TMZ, was fired off to Songz and his team Thursday by attorneys George Vrabeck and Ariel Mitchell on behalf of their client, Megan Johnson, who they allege was sexually assaulted by Trey during a party back in August 2013.

They say Johnson was at an event called "Foxwoods Liquid Sundays with Trey Songz" at the Foxwoods Resort Casino in Mashantucket, CT -- and it was there, they claim, that Megan encountered Trey in the VIP tent.

According to the letter, Johnson was having a friend take a picture of her, but in that moment they allege Trey came up from behind and pulled her breast out from her bikini top and then chanted "T***ies in the Open" four different times.

In the video, you see a woman who they claim is Johnson quickly reach up to cover her chest in embarrassment.

While Megan appears to have laughed it off, the attorneys claim she was humiliated and the incident caused lasting damage, including severe emotional distress and self-harm.

The attorneys say Megan was recently triggered by Trey's Vegas case -- which was recently dropped by authorities. The lawyers say they will drop the case if Trey settles ... for north of $5 mil.

There may be a statute of limitations problem for Megan ... the statute of limitations for this in CT is generally 3 years, although if there's a memory issue with the alleged victim where she doesn't recall the incident until she's triggered later, she may be able to try to extend that period.

They're giving Trey until May 5 to respond ... we've reached out to Trey's team, no word back yet.

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