Royal Mail staff will go on strike on Tuesday in a long-standing dispute over pay and conditions.
Members of the Communication Workers Union (CWU) will mount picket lines outside sorting and delivery offices across the country.
Efforts to break the deadlock are continuing despite the ongoing industrial action. More strikes are planned in the coming weeks.
A Royal Mail spokesperson said: "We remain hopeful of entering talks this week with the CWU through Acas to resolve our dispute on change and pay.
"This is the only way to get a resolution and secure Royal Mail's future and jobs for our people.
"On Friday October 14, we announced losses of £219 million in the first half of the year. Strike action has weakened our financial position and threatens the job security of our postmen and women.
"To give the talks the best platform to build towards an agreement, we call on the CWU to suspend their planned industrial action.
"The focus now must be on overcoming the difficulties that have prevented an agreement from being reached. We apologise to our customers for the inconvenience the CWU's continued strike action will cause.
"We are doing all we can to minimise delays and keep people, businesses and the country connected."
The CWU said its Royal Mail members have had an un-agreed 2% pay deal imposed on them, at a time when inflation is in double figures.
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