Unite is set to announce further ambulance strikes in the bitter dispute over pay and staffing.
Officials warned that walkouts could run into March after accusing the Government of refusing to negotiate.
Unite, which represents 100,000 NHS workers, said its ambulance Organising Professional Committee is meeting later today to set new strike dates.
The further dates will then be put to members to confirm.
Unite ambulance members are already set to strike in Wales on Thursday and Monday.
Life and limb cover will be negotiated locally with NHS trusts to ensure an emergency response service that genuinely reflects patients’ needs.
Sharon Graham, Unite general secretary, said: “The Government has gone from clapping NHS workers during the pandemic, to ignoring them, insulting them, and now threatening them with the sack if they fight for decent pay.
“Ministers are paying the price for this in the growing anger among NHS workers and, as a result, growing support for strike action.
“A responsible government would get around the table for real talks with the unions and get the current crisis sorted with a wage deal that matches workers’ expectations.
“Their continued failure to do so will only result in more and more strikes.”
The GMB will also announce fresh strikes by its ambulance members later today.