Thousands of Post Office workers and managers will stage a fresh strike today in a dispute over jobs, pensions and branch closures.
Members of the Communication Workers Union and Unite will walk out for the second time in two months, with further action in the run-up to Christmas not ruled out.
The unions are in dispute over the closure of the final salary pension scheme, job losses and the franchising of Crown Post Offices, the larger branches usually sited in high streets.
The Post Office said most of its network of thousands of branches will not be affected by the industrial action.
The dispute affects thousands of staff working in Crown offices, administration and supply chain roles across the UK, and the strike follows a walkout in September which the unions said was strongly supported.
CWU general secretary Dave Ward said: "The stakes have never been higher for the future of the Post Office, its workers and the communities they serve. The Post Office is at crisis point and the management and Government need to listen to the workforce.
"Staff and the public are seeing little more than a glorified closure programme from the Post Office and it cannot survive by simply cutting costs.
"We are calling for the Government, as the owner of the Post Office, to step in, halt the cuts and work with us to develop a proper strategy that will secure the future of the service."
The Post Office maintains that moving post office services to retail outlets such as WH Smith leads to longer opening hours.