A Labour peer has called for the FSA to probe claims that former non-executive directors at RBS were pressurised not to question its risky activities.
Lord Foulkes contacted the City watchdog after being privately briefed by former insiders at the bank.
He asked for a probe into whether the bank made knowingly false statements to investors about how secure its position was and if there was "intimidation".
In an article in The Observer, he suggested that if this was the case, it might lead to criminal action.
The RBS received a massive Government bailout to save it from collapse after running up £24 billion losses last year.
Former non-executive members of the RBS board were paid £72,500 a year and were required to "satisfy themselves on the integrity of financial information and that financial controls and systems of risk management are robust and defensible."
Press reports this weekend - denied by the bank - suggested that £30 billion of "toxic" sub-prime mortgages were bought for RBS by US-based traders in 2007 without the board being informed.
Lord Foulkes told the Observer there was "widespread anger among the public and Parliament that bankers in the midst of this financial crisis appear to be profiting and no action is being taken in relation to action which constitutes criminal offences."
He raised concerns that non-execs may have been subjected to "intimidation" which led them to fear they may would not be reappointed if they continued to ask searching questions about the bank's activities.
"If it were to transpire that executives were pressurised in such a way, then that is a most serious matter indeed that needs urgent action," he said.
