Five ambulance services in England will walk out on January 11 and 23.
London, Yorkshire, the north-west, north-east and south-west will be affected by the strikes, which follow action by members of three ambulance unions on Wednesday.
The January strikes will each be for 24 hours, from midnight to midnight, and involve all ambulance employees, not just the 999 response crews, as was the case on Wednesday.
UK strikes – in pictures
Many of the services’ employees are likely to be exempt from the action under emergency cover plans to be drawn up locally by each ambulance employer, working with Unison, the union said.
“It’s only through talks that this dispute will end. No health workers want to go out on strike again in the new year," said Unison general secretary Christina McAnea.
“But accusing NHS staff of making a conscious decision to inflict harm on the public by taking action this week was not the Health Secretary’s finest hour.
“Neither was it a particularly smart move for Steve Barclay to falsely accuse health unions of failing to deliver a national emergency cover plan.
"The secretary of state knew full well life and limb cover arrangements were being agreed locally by ambulance managers and unions.
“It’s time Steve Barclay stopped with the insults and fibs and called the unions in for proper talks about improving NHS pay.
Nurses strike in the UK - in pictures
“Speeding up next year’s pay review body process won’t solve the current dispute, which is about the pitiful amount the government gave health workers this year.
“The government must stop using the pay review body as cover for its own inaction. This year’s pay rise simply wasn’t enough to halt the exodus of staff from the NHS.
“The government should right that wrong with an increase better matching inflation. Only then will vacancy rates reduce, allowing the NHS to get back on track and start delivering safe patient care once more.”
After the festive break, the union will begin to ask about 13,000 staff in 10 English NHS trusts if they are prepared to take strike action in the spring.
This is because the turnout in the previous strike ballot, the results of which were announced last month, fell just below the threshold required by law.
The vote will include the other five ambulance services in England – the West Midlands, East Midlands, east of England, south-east coast and south central.
There will also be a re-vote of staff working for the Welsh Ambulance Service.
UK nurses walk out for second time threatening further strikes in pay dispute - video
Health workers belonging to Unison and employed at Great Ormond Street Hospital, Liverpool Women’s Hospital, London’s Tavistock and Portman NHS Foundation Trust and the north-west Bridgewater Community Trust are being asked to vote again.
There will also be a re-ballot of Unison members working for the NHS Blood and Transplant service.
“Today’s announcement of two more strike dates by a wider range of ambulance workers in January will add even more pressure to an already challenging situation following strike action by nurses and ambulance staff earlier in the week," said Saffron Cordery, interim chief executive of NHS Providers.
“We’ve already seen significant disruption to patient services with thousands of appointments being rescheduled or cancelled, with the fallout from this week’s strike action likely to be felt for days to come.
“And we know that ambulance staff don’t want to be striking either, but feel driven to take this step.
“The potential to continue to escalate action and for prolonged, co-ordinated strikes by more health unions in January if talks, including on pay, don’t take place is incredibly worrying.
“There are no winners in this situation. Serious talks must take place between health ministers and unions, and fast.”