Energy and water firms could be forced to be more open with the public about their operations under government proposals to extend the scope of freedom of information (FoI) laws being pushed by the Liberal Democrats.
Justice Minister Simon Hughes said private firms which were "serious contributors to household bills" and dominant housing associations should be subject to the same disclosure requirements as public bodies.
He said he was ready to "fight" to ensure that Network Rail would also be included when it is reclassified as a public body next month after the change was apparently blocked by Downing Street.
In an interview with the Financial Times and Daily Telegraph, he said he was surprised and disappointed that "as of this minute somewhere in Tory central command there is a 'we don't want to go there' with Network Rail".
A Lib Dem source said the change had been expected to be made this week but was pulled "out of the blue" by Prime Minister David Cameron, and that there was not yet "complete sign-up" across the cabinet for the wider extension.
Downing Street said that "discussions are ongoing" on both fronts.
"The question is whether we ought not to use FoI to hold to account people who are serious contributors to household bills and in which there is a huge public interest in making sure they are behaving accountably," Mr Hughes said.
"The public have a serious interest in knowing that they are getting their money's worth and the job is being done properly and safety is being applied.
"I want to push forward significant changes to open up the information about the way that public services and other services given to the public are run.
"This is about catching three big fish it is right to bring into scope: housing associations, water companies and the Big Six energy companies."