Thousands of postal workers will walk out on Easter Saturday in a dispute over closures, jobs and pay.
The Communication Workers Union (CWU) said today that 4,000 of its members at 373 post offices run directly by Post Office Ltd, known as crown offices, will strike for 24 hours.
Workers backed industrial action by almost nine to one.
They want to stop the proposed closure or franchising-out of more than 70 crown offices, as well as over pay and jobs.
A number have already been franchised to firms such as WH Smith, the CWU said, while Post Office staff have not received a pay rise since April 2011.
CWU deputy general secretary Dave Ward said management was "refusing to negotiate" and had "abused" workers' "patience and loyalty."
"This dispute is about protecting jobs and services as well as securing a fair pay increase for our members. We're saying to the public: 'If you value your post office, support these workers on Easter Saturday and beyond'."
And CWU assistant secretary for Post Office members Andy Furey said that bosses "and their ill-conceived policies are out of touch" with both staff and the communities the Post Office is meant to serve.
"A huge majority of crown office staff voted for strike action. That's a serious vote of no confidence in Post Office management.
"We want them to stop their flawed plans and instead recognise the immense value to customers of the crown office network and its staff.
"If the Post Office continues to refuse to negotiate, this strike will be the first of many."
The Post Office said it was "disappointed" with the strike, claiming that the CWU refused to understand the requirement for "critical change" across the crown network, which it said was losing £40 million a year.
The company said strike action would do nothing to change the need to build a "profitable, modern and commercially viable" crown network that does not rely on government money.
It added that its offer of a series of cash payments of up to £3,400 to be paid before April 2015 was still on the table.
Post Office network and sales director Kevin Gilliland said: "The CWU is ignoring the harsh commercial realities being faced by the Post Office and other retailers across the UK.
"Crown branches are currently losing £40m per year and this is being subsidised by public money. This cannot continue.
"The Post Office is transforming its network to improve customer experience and in turn bring in new business," said Mr Gilliland.
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