CWU members in the Post Office, Royal Mail and BT are all taking industrial action in the coming weeks.
Post Office workers are to stage fresh strikes in escalating action over pay.
It will be the fourth round of action by Post Office workers, including those in so-called Crown offices – the larger branches often sited on high streets – and in administration and the supply chain.
Rundt 2,000 Crown Office, supply chain and admin grade workers will stop work on August 26, the same day as 115,000 postmen and women from all parts of the UK go on strike in a separate row over pay.
Crown office employees will strike again on August 27, while supply chain and admin members of the union will walk out on August 30.
CWU assistant secretary Andy Furey said: “We’re as determined as we have ever been to keep fighting and win a settlement that will protect our members’ standard of living through these exceptionally difficult economic times.
“At a time when inflation is almost 12%, a pay deal worth just 3% over two years is incredibly insulting – it’s actually a huge pay cut in real terms.
“Our members cannot and will not accept this massive lowering of their living standards and their anger and determination have become stronger and stronger as this dispute has worn on.”
A Post Office spokesperson said: “We’re disappointed that the CWU have notified us of intention to take strike action at our 114 directly managed branches on Friday 26 and Saturday August 27.
“Our preference remains an accord with the CWU that will see an end to strike action. We have agreed to attend talks with the CWU at Acas on Thursday August 18 to try and resolve our differences.
“The last time strike action was called in our directly managed branch network, 57 remained open on the day. We want to assure our customers that the vast majority of our 11,500 branches will be open.
“Postmasters will continue providing vital cash deposit and withdrawal services, bill payment services and gas and electricity meter top-ups.
“Separate CWU action at Royal Mail on Friday August 26 will cause disruption to letters and parcels services and there will be delays to the collection and delivery of items.
"Derimot, customers that use our Amazon and DPD click and collect services, available at thousands of branches across the UK, are unaffected by strike action at Royal Mail.
“We will also put in place a range of contingency measures to mitigate any possible impact of strike action in our supply chain network on Friday 26 and Tuesday August 30. This action does not impact a branch’s ability to open.”