Simon Cowell is said to have asked the bands, both previous X Factor finalists, to sing on the cover of Rose Royce's 1978 hit 'Wishing on a Star'.
He was apparently concerned that this year's "average" contestants weren't enough to ensure the song becomes a chart success and so added established artists for the first time.
An insider told The Sun: "Simon and the other Syco execs want huge sales this year and weren't sure the contestants would get that on their own.
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© PA Images / Ian West/PA Wire
"Now they'll be using One Direction and JLS's combined fanbase to sell the song. It's a no-brainer and is bound to be a huge seller now."
A spokesman confirmed: "As Simon has a personal involvement in this year's charity he has asked two of the country's biggest acts to make this year's X Factor charity single the biggest of the year.
"He asked One Direction and JLS to sing on the track to give the song something extra special - and encourage all their fans to buy the single and raise lots of money for the charity."
Previous X Factor charity singles - 'Hero' in 2008, 'You Are Not Alone' in 2009 and 'Heroes' last year - have all reached number one.
'Wishing on a Star' is due to be released on November 20 and all proceeds will go to ACT & Children's Hospices UK.
JLS will perform on the X Factor results show on Sunday, while One Direction will appear the following weekend.
> X Factor finalists visit children's hospice: Pictures
> X Factor stars record charity single 'Wishing on a Star' - pictures
> One Direction, Westlife, Susan Boyle, JLS for Children in Need 2011
Watch One Direction's video for 'What Makes You Beautiful' below:
