Former Leyton Orient chairman Barry Hearn wants full public disclosure of West Ham's deal as tenants of the Olympic Stadium.
The cost of transforming the venue into a stadium ready for football has reached £272m.
West Ham will contribute £15m but the rent they will pay - reported to be £2m a year - has not been made public.
"Who is it confidential from? I can't see any reason whatsoever why it should be secret," Hearn told BBC Sport.
Hearn, chairman of Orient for nearly 20 years until selling up in 2014, wanted the club to groundshare the Olympic Stadium with West Ham and lost out in a legal battle to have the bidding process overturned.
"The actual deal West Ham has got is still confidential and our current mayor of London is refusing to reveal details," he said.
"As a taxpayer, I find that quite confusing. When people spend my money, I rather like to know what it's been spent on.
"In the absence of that information we can only speculate that it is a deal so beneficial to West Ham that it becomes questionable in its own right."
It is thought details of the deal remain confidential because much of it is regarded as commercially sensitive information.