The Voice coaches have been banned from saying that their chairs "spin" in a list of rules governing their appearance on the show, according to reports.
The Sun said that Will.i.am, Sir Tom Jones, Jessie J and Danny O'Donoghue have to describe the way their chairs move as "turning", can never call themselves judges and must describe the aspiring singers as artists.
It said that the BBC had to agree to the rules as part of a £22 million two-year deal to buy The Voice from a Dutch production firm.
An insider was quoted as saying: "Producers have given the coaches a series of strict pointers about what they can and can't say.
"One of the most important ones is that they must never say that their red chairs spin - they only turn."
The source added: "It may sound silly but these format points are really important as the BBC signed up to them when it nabbed the show and the coaches have been told they can't deviate from them.
"The Voice prides itself on its difference to The X Factor, so judges have been told the emphasis in their feedback to acts must be positive."
The BBC One show returns on Saturday with format changes.
Sir Tom Jones recently revealed that producers had suggested lines to the coaches last year, in case they didn't know what to say.