Postal workers volition onslaught connected six days successful December, including Christmas Eve, usually 1 of the busiest days of the twelvemonth for Royal Mail.
The enactment is connected apical of 4 days already announced for precocious November, astir the Black Friday buying weekend.
The Communication Workers Union (CWU) said "the livelihoods of postal workers" were astatine stake.
Royal Mail said changes to the concern were "not optional".
The long-running quality revolves astir pay, jobs and conditions astatine the privately-owned firm.
The caller strikes person been called for 9, 11, 14, 15, 23 and 24 December, the busiest clip of the twelvemonth for deliveries.
The CWU which represents much than 115,000 postal workers astatine Royal Mail, said it inactive wanted a negotiated colony with Royal Mail Group and would "continue to prosecute the institution to that end".
"But those successful complaint of Royal Mail request to aftermath up and realise we won't let them to destruct the livelihoods of postal workers," it said.
Last period Royal Mail projected a "pay-for-change" connection which would see changes to workers' displacement patterns including commencement times and Sunday moving successful speech for a 9% wage emergence dispersed implicit 2 years.
The CWU rejected the connection describing the company's plans arsenic the "Uberisation" of the postal service.
Royal Mail said: "Our penchant is for an statement with the CWU but the alteration we request is not optional.
"They should beryllium focused connected a solution to this quality for their members and the semipermanent wellness of the business, alternatively than damaging onslaught action," it said.