The date thousands of ambulance workers can begin to vote on whether to take strike action has been announced.
The GMB union said a ballot will open on 24 October for ambulance staff at 11 trusts across England and Wales.
More than 15,000 members can vote on industrial action in the pay dispute, with the GMB saying any strike could take place before Christmas.
The Department of Health and Social Care (DHSC) urged unions to "carefully consider" any impact on patients.
A GMB spokesperson said ambulance staff were angry about the government's imposed 4% pay rise, which they said was a "massive real terms pay cut".
Workers from London, East of England, East and West Midlands, North East, Yorkshire, North West, South Central, South East Coast, South West and Wales ambulance trusts will take part in the ballot, which closes on 29 November.
Rachel Harrison, GMB national officer, said: "Pay has been systematically slashed for more than 10 years and we now face the worst cost of living crush in a generation.
"Meanwhile vacancies are at record highs and we have the worst A&E delays ever – and it's not even the winter flu season yet."
She added that members "feel they are unable to deliver safe standards of patient care".
A DHSC spokesperson previously said industrial action was a "matter for unions".
The spokesperson added the government valued the "hard work of NHS staff" and had given more than "one million NHS workers a pay rise of at least £1,400 this year".
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