Postal workers' leaders have made a last-ditch attempt to avert a national strike, warning they would have "no option" than to press ahead with action if progress is not made in the next few days.
The Communication Workers Union (CWU) will set strike dates tomorrow if a deadlocked row over pay, jobs and conditions is not broken.
The union will have to give seven days' notice of a strike, so the earliest a walkout could be is on October 22.
Business secretary Lord Mandelson warned that a national postal strike would be a "suicidal act".
Postal workers have voted by three to one in favour of industrial action, but the union held back from announcing strike dates, instead declaring it was giving one last chance to avert a national walkout which would cripple mail deliveries across the country.
Dave Ward, the union's deputy general secretary, said yesterday: "Postal workers do not want to take strike action but neither are they prepared to put up with continuing attacks from a management which is failing. We have today written to Royal Mail making it clear that the CWU is ready to issue notice for a national strike as voted for by three quarters of postal workers.
"More importantly, we have offered what we believe is a genuine alternative to reach a lasting agreement. This is an opportunity to avoid a national strike, restore customer confidence and resolve the concerns of staff. If Royal Mail really is sincere about reaching an agreement we expect them to take up this offer for the interests of all involved in the mail industry."
The CWU called for a new benefits package to reward postal workers, urged Royal Mail to step back from imposing changes and said a three-year agreement should be reached aimed at providing long-term stability for the business, employees and customers.
Royal Mail managing director Mark Higson said the union had raised a number of issues, including a demand for more money.
He added: "If the union are serious about resolving this dispute they should immediately lift the threat of strike action, including the strikes planned for tomorrow in London, which have hung over our customers for far too long. Royal Mail is very disappointed that the CWU continues to threaten customers with national strike action and still fails to honour repeated offers to call off all strikes even though Royal Mail told them two weeks ago there would be no further changes this year. Since then, the union have called strikes in more than 150 delivery offices and still continues to threaten a national strike."