Around 80,000 nurses have put their name to a petition calling on the NMC to reverse plans to increase its registration fee from £76 to £120 - a rise of almost 60 per cent.
The RCN petition came as health secretary Andrew Lansley ordered an independent audit of the proposed fee rise, saying the regulator had a responsibility to assure its registrants that the decision had been made 'on a sound financial basis'.
In a letter to NMC Deputy Chair Professor Judith Ellis, Mr Lansley said the 'fee increase for registrants is difficult to justify at a time of pay restraint', suggesting an external audit is the best way to ensure the plans are 'robust and future proof'.
'I believe it is vital that the NMC seeks independent verification of its case for a fees rise, taking into account the lessons learned from the Council for Healthcare Regulatory Excellence strategic review about previous failings in financial management,' he said.
In a joint statement, the RCN, the Royal College of Midwives and Unison said they were pleased the secretary of state had intervened.
'We hope to see the terms of reference for the audit as soon as possible, and that those terms will be wide-ranging enough to deliver the change needed if the NMC is to be financially sustainable. It is also only right that the deadline for submissions to the NMC's current consultation should be extended so the results of this audit can be taken into account.'
The NMC said it had received 'external assurance' that the business case for the fee rise was financially sound. It added this advice was taken into account in proposals set out in June's consultation document.
'We have actively shared and continue to share information about the NMC's financial position and the proposed fee rise with the DH, the Council for Healthcare Regulatory Excellence and unions,' the NMC said. 'Council remains concerned that further delays in implementing a fee rise will have a negative impact on public protection.'
Last month, the DH announced a new NMC chair will take up post in the autumn for an initial period of 18 months. Former civil servant Mark Addison has 'a strong record in improving performance at a number of public bodies', the department said. The NMC has raised concerns about the selection process and imposition of a candidate by the DH.