A Jagged Edge fan claims his favorite band stood him up at the altar last month ... when they failed to perform at his wedding -- but the group says he's simply pointing the finger at the wrong guys.

The groom at the center of the controversy is Victor Diaz ... who claims he wanted to surprise his fiancee by getting JE to perform their famous "Let's Get Married" song at their wedding on November 19.  Diaz claims he reached an agreement with the band's reps ... and shelled out $10k for the deposit and other costs -- but the band never showed up.

But ... the band says they were never aware of the gig -- telling TMZ Diaz must have been dealing with someone who falsely posed as a representative of the band.

Diaz isn't buyin' it ... and believes the band decided to flake on the wedding when they got an offer for a higher paying gig on the same weekend.

Diaz says he's preparing to sue Jagged Edge, the record label and JE's management company -- telling TMZ, "They humiliated me and cost my wife her dream."

A rep for Jagged Edge tells us, "They are very heartbroken and sad that [Victor's] wedding got destroyed due someone using our name without permission."

The rep adds, "As far as court goes ... if the guy does decide to sue, good luck, because we didn’t agree to anything and he will see he had a forgery contract."