Royal Mail revealed plans to reduce 6,000 jobs by next August.
The postal service blamed ongoing protests and mounting business losses.
It had begun informing staffers about the plans, which will trim its headcount by 10,000.
The majority of the downsizing will be done through redundancy, with the remainder accomplished through natural attrition.
Royal Mail also stated that it estimates its full-year losses to exceed £350 million.
It cited “the direct impact of eight days of industrial action” along with fewer parcel delivery volumes as the reason.
However, the company warned that losses might exceed £450 million “if customers move volume away for longer periods” following the walkout.
CEO 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.”
Currently, the organization employs 140,000 employees.
Royal Mail workers have started a new set of strikes over wages and conditions, which will last 19 days, including Black Friday.
The employees are members of the Communication Workers Union.
Dave Ward, the CWU’s general secretary, said the move “is the result of gross mismanagement and a failed business agenda of ending daily deliveries.”
He also cited “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.
Need Career Advice? Get employment skills advice at all levels of your career
“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 continue to strike “the loss for the full year would increase materially and may necessitate further operational restructuring and headcount reduction”.
Royal Mail also stated that it will have to get into talks with the union because its legacy voluntary redundancy policy, which provides up to two years of salary, “is now unaffordable.”