Royal Mail has announced plans to cut 10,000 jobs by next August, blaming ongoing strike action and rising losses at the business.
The postal company said it will begin notifying workers of its plan, which includes up to 6,000 redundancies.
Apart from the redundancies, the firm will cut roles through natural attrition, for example by not replacing workers who leave.
Royal Mail also said it expects its full-year losses to hit £350m.
It said this included “the direct impact of eight days of industrial action” as well as lower volumes of parcels being posted.
But the firm warned that losses could reach as much as £450m “if customers move volume away for longer periods” following strike action.
Royal Mail’s chief executive Simon Thompson said: “This is a very sad day. I regret that we are announcing these job losses. We will do all we can to avoid compulsory redundancies and support everyone affected.”
Royal Mail workers, who are members of the Communication Workers Union, began a fresh round of strikes this week over pay and conditions which will include 19 days of industrial action, including Black Friday.
The next strike date is scheduled for 20 October followed by a further walk-out on 25 October.
The CWU’s general secretary, Dave Ward, said Royal Mail’s announcement “is the result of gross mismanagement and a failed business agenda of ending daily deliveries, a wholesale levelling-down of the terms, pay and conditions of postal workers, and turning Royal Mail into a gig economy style parcel courier”.
But Mr Thompson said on Friday: “Each strike day weakens our financial situation.
“The CWU’s decision to choose damaging strike action over resolution regrettably increases the risk of further headcount reductions.”
Royal Mail said that if workers go ahead with further walk-outs “the loss for the full year would increase materially and may necessitate further operational restructuring and headcount reduction”.
During the first half of its financial year, Royal Mail said strike action cost the business £70m, leading to an operating loss of £219m compared to a £235m profit last year.
But Mr Ward responded: “This announcement is holding postal workers to ransom for taking legal industrial action against a business approach that is not in the interests of workers, customers or the future of Royal Mail. This is no way to build a company.”