Half of this year's 12 X Factor finalists were approached to audition for the show.
A spokesperson for the show told Newsbeat all acts had to go through the same process but that some had been asked by researchers to take part.
Producers insist that the judges did not know whether acts had been invited to audition when they were deciding whether to send them through.
http://www.bbc.co.uk/newsbeat/19835534