LONDON (Reuters) – More than 115,000 workers at Britain’s Royal Mail began the first of four days of strike action on Friday in a pay dispute which the postal group said was likely to cause significant disruption for customers.

It is the latest in a spate of labour stoppages to hit Britain as workers demand higher wages in the face of a cost-of-living crisis, with energy bills soaring and inflation projected to exceed 13% later this year.

“We are going to fight very hard here to get the pay rise our members deserve,” Communication Workers Union General Secretary Dave Ward told Sky News.

Royal Mail says it has offered a 5.5% pay rise for CWU-grade workers, its biggest increase in years.

The union, which said the strike was the biggest industrial action taken by workers this summer in Britain, disputes this and says the company has imposed a 2% pay increase on workers, and offered a further 1.5% subject to changes to terms and conditions.

The centuries-old British postal and delivery service apologised to its customers for the disruption and said it had put in place contingency plans, but could not fully replace the daily duties of its frontline staff.

Royal Mail warned earlier this month that it could post a loss for its business in the United Kingdom in the 2022-23 fiscal year if the strike went ahead. Further walk outs are planned for Aug. 31, Sep. 8 and Sep. 9.

Royal Mail Chief Executive Simon Thompson said the business needed to change its working practices to reflect the fact that it now delivers more parcels than letters and the parcels delivery market is very competitive.

“Royal Mail is a company that society wants to exist… but we need this change so we can turn into a parcels business so we can flourish,” Thompson told British radio broadcaster LBC.

We want to pay our team more. The more change, the more pay.”

(This story corrects source of Thompson comments to LBC, not BBC.)

(Reporting by Farouq Suleiman and David Milliken; Editing by Toby Chopra and Frank Jack Daniel)