TMZ Hip Hop obtained a copy of the letter Jon's team fired off Monday to the concert-promoting corporation ... detailing his efforts to reach a financial agreement over the incredibly popular Las Vegas festival.

Jon says he and Live Nation began talks back in May 2022 through one of his lawyers, Doug Davis, and assumed Live Nation would do the right thing. We're told he didn't want to push too hard because he was focused on ensuring last year's festival -- headlined by Jon, Usher and Ludacris -- was a success.

Now it's a year later, and Usher recently announced the lineup for this year's lineup -- boasting megastars Chris Brown, Missy Elliott, 50 Cent, Nelly ... but no Lil Jon!!!

In the letter, Jon's powerhouse attorney Ed McPherson compares putting on a "Lovers & Friends" fest without Jon ... to having a "Don't Stop Believin'" festival without Journey, or a "Cheeseburger in Paradise" festival without Jimmy Buffett.

It's an obvious attempt to put the dispute in terms Live Nation's attorneys will understand.

Sources connected to Jon tell us he's been hoping to avoid litigation, and for months, attempted to reach a settlement.

For the record, Jon readily admits his "Lovers & Friends" -- from his 2004 "Crunk Juice" album -- is a cover of Michael Sterling's 1991 song, but insists his version is the one that became "omnipresent in the Black community" ... so much so, Live Nation's slapped the name on its festival.

Bottom line ... Lil Jon believes they owe him big, because Live Nation's trading off his hard work to create such a lasting hit.