The reality star, who came 67th in the poll won by Contostavlos, announced on Twitter that she would be attending Tuesday's (May 3) party, but was absent from the event itself.
It has since been claimed that security were instructed to turn Mecklenburgh away because the 'Young' singer's team would only allow her to attend if no-one from TOWIE was at the bash.
"She was told if she turned up Tulisa wouldn't be allowed to," a source told OK. "And they really needed their winner at the event."
Though Mecklenburgh has not confirmed the snub, she did tweet on the night of the party: "People need to remember where they come from !!!!! I'm soo upset."
Mecklenburgh's boyfriend and TOWIE co-star Mario Falcone yesterday blasted Contostavlos's victory, writing on Twitter: "Do not understand how Tulisa won FHM 100 sexiest women... Must be a fix!!!"