Striking Royal Mail workers are continuing industrial action into a second day, as Gordon Brown calls for negotiations to end the union's "self-defeating" strategy.
Delivery offices and collection units are striking today after staff at mail centres and network distribution units walked out yesterday.
It comes despite the government calling on both the Communication Workers' Union (CWU) and Royal Mail to accept independent arbitration from Acas. The union is angered by Royal Mail's refusal to secure complete agreement on the implementation of a 2007 pay and modernisation deal.
Yesterday the CWU announced a further round of industrial action for next week beginning on Thursday October 29th. Around 30 million letters are expected to be delayed, Royal Mail said today.
Business secretary Peter Mandelson said it would be wrong for the government to intervene.
"I'm not sure that my intervening would be welcome by both sides. Both sides within the Royal Mail itself need to resolve this," he told the BBC.
But the prime minister called for management and union leaders to continue negotiations.
"I think instead of striking the workers and the management should be sitting around the table getting an end to this strike. You've got to look at the future of Royal Mail here," Mr Brown said.
"This is self-defeating. I believe that by discussing and negotiating, if necessary bringing in an arbitrator like Acas, we can get a solution to this problem.
"We're doing what we can to make possible the resumption of talks between the management and the workforce."
A poll for the BBC suggested 50 per cent of respondents were sympathetic to the union. Only 25 per cent backed Royal Mail.