Ray J Calls Out Mario & Wale as 3rd Best Singer Behind Chris Brown & Usher

Ray J isn't backing down from challenging Mario in a singing battle ... despite his opp not taking the competition too seriously.

We caught up with Ray in NYC mid-morning Tuesday, where he was advocating for a TMZ After Dark and Brunch Tours in the Big Apple -- a move which definitely has a nice ring to it.

After all, Ray has become quite the Hollywood draw with our bus patrons, so an expansion may be on the horizon!!!

Back to the matter at hand ... Mario and Ray are currently in a volley of words about singing superiority, and Ray demands some respect be put on his name.

Ray recently attempted to crash Wale's homecoming stage in Baltimore alongside Mario, only to be stiffed ... so now he has smoke with the "Lotus Flower Bomb" rapper as well!

Like Mario, Ray's also seen Brandy's comments about him not taking his craft seriously, but tells us he's turning over a new leaf -- by getting her to retrain his vocal chords.

Brandy's currently on tour with Monica -- and already has to approval of Mario, so Ray has to lock in or get passed by.