Hopefuls of the ITV talent show are said to have been instructed not to reveal any information about Cowell and his fellow judges, or the audition process.
A three-page document has been sent to finalists, barring them for life from revealing that it exists in the first place, according to The Mirror.
Acts must reportedly sign the deal with Cowell's firm Syco, banning them from making "any disclosure to the press" during the show and after "termination".
A source stated: "Compared to other TV show contracts, the scale and sheer number of the confidentiality clauses is highly unusual."
Hopefuls must not speak to the media about "any of the talent... including for the avoidance of doubt Simon Cowell, David Walliams, Alesha Dixon and Amanda Holden".
They are also barred from revealing "any incidents taking part in any house or home wherever in the world" belonging to any of the judges.
Also reportedly out of bounds is discussing the audition or selection process, along with posting updates on social networks without Syco's permission.
Contestants have been told to read the agreement "very carefully before signing it".
A second insider said: "It must seem a pretty draconian contract, but contestants sign it when they get to the latter stages. If they don't abide by it, they could be sued."
Britain's Got Talent returns Saturday (May 4) at 7.15pm on ITV.
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