More time has been given for 55,000 people to complain about being mis-sold payment protection insurance (PPI).
The Financial Services Authority has extended the normal six-month deadline for people to go to the Financial Ombudsman Service (FOS) if a firm turns down their original complaint.
The temporary rule benefits those whose complaints were first rejected between 28 November 2009 and 28 April 2010.
They now have five months more to complain, until 27 October 2010.
The FSA said the measure was being put in place so that potential complainants were not disadvantaged by a delay in the regulator's own plans to revamp the way firms are obliged to deal with new PPI complaints.
Mis-selling of PPI, which is supposed to help people meet their loan repayments if they fall ill or lose their jobs, is currently the biggest source of unresolved problems in the financial services industry.
The FOS reported recently that they accounted for 30% of all the new complaints it dealt with in 2009-10.
In September 2009, the FSA decided to get tough, ordering banks and other sellers of PPI to reopen previously rejected complaints about mis-selling of the insurance, which it now thinks could number about 500,000.
It also told firms to improve the way they dealt with new complaints.
However, implementation of its plans has been delayed because of the many objections sent in by lenders, brokers and other sellers of PPI, which are now being considered by the FSA's staff.
The regulator still hopes to have a new set of industry rules in place by the end of this summer.
But in the meantime, it wants to ensure that all those whose complaints had been rejected by firms since the end of last November will be encouraged to go to the FOS if they want to complain further.