Hundreds of G4S security staff who deliver cash and coins have voted to strike in December, prompting fears of shortages ahead of Christmas.
The industrial action could impact the supply of cash and coins at banking clients such as Barclays, HSBC and Santander, and supermarkets including Tesco, Asda and Aldi.
The GMB union said it will be the first ever strike at G4S after union members voted to walk out, with a 97% vote in favour of action.
The security operator and outsourcing firm said it has “contingency plans” to mitigate disruption if the strike goes ahead.
G4S Cash Solutions initially offered members a part pay freeze and have since tabled an offer of a 4% increase and lump sum bonus based on contracted hours.
The security giant was taken over by American firm Allied Universal for £3.8 billion last year following a takeover battle.
Eamon O’Hearn, GMB national officer, said: “There are low paid workers doing a dangerous job, transferring the cash so many of us still rely on every day.
“G4S Cash staff provide an absolutely vital service. If they walk out, we can expect genuine cash shortages over the festive period.”
A G4S spokesman said: “We are continuing to engage with our employees and their union and hope to reach an amicable agreement without the need for industrial action.
“In the event of a strike, we have contingency plans to minimise disruption to cash services across the country.”
The firm stressed that its UK cash drivers have received pay of £13.08 an hour for 2022 after a pay deal was agreed with the GMB from January.