A committee of MPs has ordered the Financial Conduct Authority to hand over its report into Royal Bank of Scotland’s restructuring unit, saying the regulator had "lost control".
The FCA has until Friday to either publish or send its report into RBS to the Treasury select committee.
Versions of the report have already been leaked and parts of it published in the press.
The committee's decision means that if the regulator fails to hand over the report, it can be held in contempt of Parliament.
Nicky Morgan, the committee's chairman, said: "A version of the report is now in the public domain. The FCA has completely lost control of the publication process.
"If the FCA doesn’t publish or provide the report by Friday, it will have breached an order of the House of Commons and may be found in contempt of Parliament.
"The committee will meet when Parliament returns on Tuesday 20 February. At that meeting, I will be asking members to agree to publish the final, unredacted report under parliamentary privilege as soon as possible."
FCA chief executive Andrew Bailey has said there are legal reasons why the full report has not yet been released, including the need to get consent from everyone who was referenced in the report or who gave information used in it, and the need to give those criticised the chance to respond.
RBS’s global restructuring group was a division that dealt with small and medium sized business customers in the UK. It has been accused of mistreating its customers and pushing viable businesses into distress.
One memo from 2009 published by the committee in January and written by a junior manager in the GRG unit said: "Sometimes you have to let customers hang themselves. You have then gained their trust and they know what’s coming when they fail to deliver."
Last month the man who led the FCA-commissioned investigation into the bank has said he was "disappointed" by RBS’s response to his findings.
Promontory Financial Group’s Tony Boorman said the bank’s counterarguments did not stand up. "If you look at some of the arguments they have put forward you will see they don't bear much scrutiny," he said.
"They draw attention to the fact that in some of the cases the fees were not levied or calculated but if I say to you I am going to quadruple your fees tomorrow, you may take a whole series of steps. Whether you do it or not is not the point. Threatening violence is nearly as serious as carrying it out."