Actors' union Equity has accused the production company behind BBC talent show The One and Only of exploiting its tribute acts by failing to pay them.
Graham Norton (centre) hosted the BBC One talent show
Endemol was "happy to exploit the dreams of aspiring performers without offering them a penny", Equity said.
Endemol, which also makes Channel 4's Big Brother, has denied being at fault.
"We have taken independent advice about this in order to ensure we are acting fairly, responsibly and in line with common practice," the company said.
"We're surprised that Equity has issued a press release rather than contacting us directly."
A BBC spokeswoman declined to comment.
Katy Setterfield, a Dusty Springfield tribute singer from High Wycombe, Buckinghamshire, won the BBC One contest.
Her prize was a three-month contract to appear in a high-profile stage show in Las Vegas.
Equity claims Endemol may have acted illegally by having the contestants sign contracts that waived their protections under working time laws.
Despite "numerous approaches" from the union, Equity said, "they have refused to pay even the smallest possible fee to the 24 contestants".
Unlike The One and Only, previous BBC talent shows How Do You Solve a Problem Like Maria? and Any Dream Will Do were made in-house by the BBC.
Equity said the corporation had "acted honourably" in giving the contestants on those shows "proper industry-standard contracts".