Workers in the country's biggest post offices will stage a fresh strike today in a bitter row over jobs, pay and branch closures.
Members of the Communication Workers Union at hundreds of Crown offices will walk out for the day, the fourth round of industrial action in recent weeks.
The union is opposed to plans to franchise 70 of the branches and close some others, saying hundreds of jobs will be affected.
The dispute also involves pay, with the CWU saying its members have not received a wage rise for over two years.
The Post Office says the Crown offices - the larger branches usually sited on high streets - are losing £40 million a year and has accused the union of refusing to accept economic realities.
But the union said it believes the company is trying to meet Government targets by "drastic" cost-cutting.
Picket lines will be mounted outside offices across the UK today, with the union expecting strong support for the walkout.
Dave Ward, CWU deputy general secretary, said: "This Government promised no programme of post office closures, but these plans would cut 20 per cent of the Crown network. This is under a minister - Jo Swinson - who campaigned against franchising before getting a government position.
"The pay offer is nothing like what the Post Office is trying to make out. It's conditional on accepting 76 Crown Post Office closures and over 800 job losses. The second and third lump sums are dependent on unachievable targets so are very unlikely to ever get paid. Even if they are paid, they would be significantly less than the publicised figure because many workers are part-time and hundreds would have lost their jobs.
"The Post Office and Government are ignoring the wishes and views of people who work in the Crown network and the customers who value these post offices. Staff voted by nine to one in favour of strike action - a resounding rejection of the company's plans on closures and pay - yet they are being ignored.
"Tens of thousands of people have signed petitions in communities across the country opposing the closure and franchise plans. These are valued services which handle significant amounts of work.
"We firmly believe that a solution could be found if the Post Office was prepared to sit down and negotiate a meaningful and mutually agreeable solution. Ploughing on and further angering their staff and customers is no good for anyone."