Thousands of Post Office workers have begun a five-day walkout, joining strikes by key air and rail staff days before Christmas.
The Communication Workers Union (CWU) said around 3,500 workers would take part in its industrial action, hitting hundreds of Crown Post Offices.
The five-day CWU strike, which begins today (19 November), is over job losses, the closure of a final salary pension scheme and the franchising of Crown Post Offices.
Action at the Post Office coincides with disputes among rail and air workers in disputes over issues such as jobs, pay, pensions and safety.
CWU assistant secretary Andy Furey said: "Our members want the Post Office management to pause its closure and privatisation programme, hold off on its planned pensions changes, and commit to sitting down with us and with the other key stakeholders of this Great British institution and, together, construct a lasting vision."
However, a Royal Mail spokesman said: "There will be little or no impact on Royal Mail as a result of the CWU strike at the Post Office. Deliveries will carry on as normal and the last posting dates for Christmas remain unchanged."
Meanwhile, RMT members at Southern Railway will strike over the next two days in a dispute over the role of conductors.
British Airways cabin crew belonging to the Unite union are due to strike on Christmas Day and Boxing Day over a pay dispute.
Talks aimed at averting the British Airways strike are due to be held on Monday (19 November) at the conciliation service Acas.
Unite members employed by Swiss air cargo handling firm Swissport as baggage handlers and other ground staff at 18 airports across the UK are set to walk out on Friday and Saturday over pay, although talks will also be held at Acas on Tuesday.