Strikes by rail and Post Office workers are "solidly supported" according to unions.
Southern Railway RMT members have begun a 48-hour stoppage in a long-running dispute over the role of conductors.
Members of the Communication Workers Union will strike for five days this week, including Christmas Eve, in protest at job losses, the closure of a final salary pension scheme and the franchising of Crown Post Offices.
The union said there was strong backing for its campaign from the public.
General secretary Dave Ward accused the management of rejecting a peace offer and warned post offices will cease to exist on the high street if the planned closure programme continues.
Post Office group network and sales director Kevin Gilliland said: "It will be business as usual in almost all of our network, with over 50,000 Post Office people on hand to support customers as they make their preparations for Christmas."
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