A rail workers' union has made a formal complaint after claiming it was denied information about the tendering for a new South East train franchise.
South Eastern Trains has run the service removed from Connex
The Rail, Maritime and Transport Union (RMT) said the Strategic Rail Authority (SRA) was denying it information.
The Integrated Kent Franchise includes routes run by South Eastern Trains since Connex was sacked two years ago.
An SRA spokesman said there was "no secrecy whatsoever" and only sensitive commercial information was withheld.
The Strategic Rail Authority (SRA) stripped the French group Connex of the franchise in June 2003, giving poor financial management as the reason.
Regional trains have been operated by government-run South Eastern Trains, a subsidiary of the SRA, since then.
Four bidders have been selected to compete for the Integrated Kent Franchise, which will provide services to Kent, south east London and parts of East Sussex from early next year.
They are Danish State Railways, GNER, FirstGroup and a consortium of Go-Ahead Group and Keolis.
"The public has a right to know what rail services the preferred bidder will be expected to deliver, as well as the fare levels and the amount of public subsidy involved," said RMT boss Bob Crow.
He said the RMT would rather the whole process was abandoned because South Eastern Trains has been operating more efficiently in public hands.
"The cloak of secrecy suggests that commuters and rail workers have good reason to be worried about the fate of their rail services," he said.
The SRA spokesman said there had been extensive consultations with railway stakeholders before the tendering process, which led to about 2,000 replies being considered and changes made.
"The one part of the process we don't release involves the bidding companies revealing commercially confidential information," he said.
"We are not asking to see the bids but to be allowed to know what the bidders are bidding for," argued Mr Crow.