Postal workers' union chiefs are poised to announce the first national postal strike in a decade after talks to avert action ended without agreement.
Any national postal strike would be the first since 1996
Leaders of the Communications Workers Union (CWU) met postal chiefs on Wednesday, when Royal Mail bosses said they could not raise a 2.5% pay offer.
Both sides say they remain willing to talk in order to break the deadlock.
However if no fresh talks take place on Thursday then the union is expected to announce dates for industrial action.
The union has rejected a 2.5% pay offer and has called for changes to the Royal Mail's modernisation plans, which it believes will cause up to 40,000 job losses.
A ballot of union members rejected the pay offer and supported a campaign of industrial action.
Members of the CWU executive from different parts of the country are discussing their next move.
Should a strike go ahead then it would be the first national walk-out in the Royal Mail for 11 years.
If talks do not resume on Thursday, then the CWU executive could announce dates for industrial action, which would impact on deliveries around the country.
The CWU would have to give at least seven days' notice of strike action, Royal Mail said.
The situation comes after Royal Mail lost a contract worth £8m from online trader Amazon.
Royal Mail officials said the contract loss showed that it had to improve its efficiency still further to be better able to compete with its newer rivals in the postal delivery industry.
Discussing the possibility of a strike, Millie Banerjee, who chairs the watchdog Postwatch, said: "The worry really is for the industry, that once you go away from using mail you may never come back. So, you know, it is very important to avert this strike."
And Clive Davenport, of the Federation of Small Businesses, said: "A lengthy postal strike would be devastating for small businesses.
"A cheque delayed in the post can mean the difference between life and death for a small business, which means that this strike cannot be allowed to go ahead.
"We call on both sides in this dispute to reach an agreement to prevent the strike."