The girl group are rumoured to have joined the lineup for the London 2012 event on Sunday, August 12.
© PA Images / Ian West/PA Wire
The performance would be the band's first live performance since 2008, but Mel B has allegedly given organisers a set of instructions.
"The delay has nothing to do with Victoria or Mel C - it's down to Mel B," a source told The Sun.
"She's told organisers that if they want her at the show they are going to have to fork out for a stack of unreasonable demands.
"She wants her friends and family flown from all over to see the gig and wants them to have backstage access. And her rider, which includes a demand for a personal stylist to be flown wherever she goes, is ridiculous."
Victoria Beckham had previously been cited as the one member who was reluctant to reunite for the gig.
A list of performers for the closing ceremony leaked to the media last week, which included Take That, Jessie J, The Who, Elbow and Russell Brand among others.
