Royal Mail workers are to stage six fresh strikes next month, including on Christmas Eve, in the long running dispute over pay, jobs and conditions, the Communication Workers Union (CWU) announced on Thursday evening.
The CWU said its members will walk out on December 9, 11, 14, 15, 23 and 24.
This is in addition to strikes already notified for November 24, 25 and 30, and December 1.
A CWU spokesperson said: "The CWU want a negotiated settlement with Royal Mail Group and will continue to engage the company to that end.
"But those in charge of Royal Mail need to wake up and realise we won't allow them to destroy the livelihoods of postal workers."
A Royal Mail spokesperson said: "Our preference is for an agreement with the CWU but the change we need is not optional.
"They should be focused on a resolution to this dispute for their members and the long-term health of the business, rather than damaging strike action."
On Wednesday, the CWU accused Royal Mail of “gross mismanagement” after talks aimed at resolving a strike collapsed.
Dave Ward, general secretary of the Communication Workers Union (CWU), accused the Royal Mail Group chief executive Simon Thompson and the board of creating financial problems by continually engaging in “dramatic errors of judgment”.
Mr Ward said: “No business making record profits of £758 million in May this year should be losing over £1 million a day in a matter of weeks without gross mismanagement.
“The truth is that the current senior leadership of Royal Mail have been treating employees, union representatives or future investors with a lack of integrity and transparency.”
A Royal Mail spokesperson said that strikes would cause “more damage to the business and make our improved 9 per cent pay offer over two years less affordable”.