Morghan Medlock just filed suit against Weezy for what she claims is wrongful termination, retaliation and a number of unlawful practices that she says she was subjected to when he canned her earlier this year ... just because she went to go help her injured son.

According to the docs, obtained by TMZ, Medlock describes a trip to Vegas she tagged along for during Memorial Day weekend -- for which she says she was doing her job (AKA, cooking all LW's meals, etc). At this point, Medlock says she'd had the gig almost 2 years.

Things were going swimmingly, that is ... until Medlock says she was notified of a head injury her 10-year-old had sustained that left him hospitalized. Obviously, Medlock wanted to get back to L.A. ASAP -- but claims Wayne and co. were screwing up the flight back over shenanigans ... namely, that Weezy allegedly delayed things by toking up on the aircraft.

Instead of standing around and waiting for them to get their act together, Medlock says she hightailed it out of there on a separate flight -- notifying Wayne's assistant of the situation and assuming they'd understand. Instead, she claims she was terminated.

Medlock says after she left, Wayne's team kept asking her if she was quitting -- to which she says she clearly responded, "No." After her son was dealt with, Medlock says she tried getting back into the swing of things as head chef -- but claims she got the cold shoulder.

Eventually, Medlock claims somebody on Wayne's team texted her an ungraceful goodbye message, and she was later formally told she was being let go ... with a message from Wayne saying, "tell Chef Morghan this isn't going to work" -- or so she claims in the suit.