The mother-of-two, who has recently announced she is pregnant with her third child, took offence to Cowell's comments, where he expressed doubts Sam could have the same success as previous X Factor contestants.
'She will have a very succesful debut album. [Is she] going to be as good as the final year we did? No. That was a very special year. I would love to find another Olly Murs or something similar to Olly.'
And despite Cowell not explicitly referring to Olly or Sam's looks, the former prison officer jumped on the mogul for being shallow.
'X Factor has had so many joke acts and not people that had potential. People that have had potential who have maybe been a bit fatter or older or not looked right, they need to start looking at those people because then you get someone like me.'
Sam also accused the talent contest of being too snobby, with singers who were too 'cruise ship or too clubby' being overlooked.
'I think they need to look a little bit further and it needs to be less shallow and they might be alright.'
Sam plays a dangerous game in criticising Cowell, who has openly cut off former contestants who have acted or spoken out against him.
James Arthur, who was guided to success by mentor Nicole Sherzinger, has certainly got on Cowell's bad side, with Simon saying of the star: 'I think James, unfortunately, has had so many issues with what he has done publicly - which is a real issue for me. Somebody should have told him to shut up and just put the records out.'
Arthur received a huge backlash from the public and the press after a homophobic rap rant which saw him call rapper Micky Worthless a 'f***ing queer.'