An influential committee of MPs is putting more pressure on the UK's financial watchdog to publish a report into misconduct at RBS.
The Treasury Committee said it could use "formal powers" to demand publication of a Financial Conduct Authority report leaked to the BBC.
The FCA has refused to publish the full report, which scrutinised RBS's small business Global Restructuring Group.
The FCA has said it will publish a detailed summary of the report.
Nicky Morgan, chair of the Treasury Committee, wants to appoint an independent legal adviser to scrutinise the detailed summary and compare it with the report.
She said that if the FCA did not accept Andrew Green QC as an independent legal adviser, the committee might look to force the FCA to publish the report.
The committee will also force publication if he concludes that the detailed summary is not an accurate representation of the full report.
The FCA has already published a short summary.
Analysis: Joe Lynam, BBC business correspondent
The Treasury Committee has twice called for the full report into the activities of GRG to be published by the FCA. That request has been refused, twice.
Now this key group of MPs is ratcheting up the pressure on the City watchdog.
In her letter, committee chair Nicky Morgan says her committee may compel the FCA to publish the report which found widespread abuse by GRG on its own small business customers.
The FCA says that it was never its intention to publish the damning report, which the BBC has seen in full.
But this creative solution by the Treasury Committee to allow one of its special legal advisers to assess the 300-plus page report and report back may satisfy both sides in this standoff - and GRG's victims as well.
The leaked report said that RBS's Global Restructuring Group (GRG), a department ostensibly set up to help companies in trouble, mistreated many of its clients.
It found that some form of "inappropriate action", such as interest charges being raised or unnecessary fees added, was taken by GRG in relation to 92% of viable firms.
RBS has denied systematically abusing its customers.
'Fair and balanced'
An FCA spokesman said the regulator welcomed "further dialogue" with the Treasury Committee on providing assurance about the publication of the summary.
He added: "The FCA has committed to publishing a detailed summary of the GRG report.
"To provide assurance on the summary, we previously asked an independent external counsel to confirm that it is a fair and balanced account of the full report's findings."
Lord Cromwell, who co-chairs the All Party Parliamentary Group on Fair Business Banking, said that even after the detailed summary is given "questions will inevitably remain as to what has been kept secret and why... and who has the whip hand - the regulator or the banks?"
RBS's Global Restructuring Group operated between 2005 and 2013 and at its peak handled 16,000 companies.
The unit would step in when businesses had missed a loan repayment, or had a notable dip in sales or profits, and was marketed as a turnaround specialist.
But the FCA report found that companies placed in the group had little chance of getting out of it. Only 10% returned to the main RBS bank intact.
At the end of 2014, 69% of firms were still in the successor to GRG.
Many of those businesses remained tied into complex loans with the bank in the form of derivatives linked to interest rates, from which it is often too expensive to leave.
RBS said it had apologised for previous mistreatment of some customers and had taken steps to put things right, including a new complaints process and an automatic refund of complex fees paid by these customers.