(Bloomberg) -- UK postal services over Black Friday and the build up to Christmas are set to be disrupted after a trade union rejected what Royal Mail called its “best and final offer.”

The Communication Workers Union, which represents 115,000 Royal Mail staff, will strike Nov. 24 and Nov. 25, it said Wednesday. Unless an agreement is found, further strikes will take place on Nov. 30 and seven dates in December including Christmas Eve. 

Royal Mail, a part of International Distributions Services Plc, said it offered a pay rise of as much as 9% over 18 months along with a profit-sharing program for workers. 

IDS shares fell 4.1% as of 2:26 p.m. in London. The stock has lost more than half its value in 2022.

Strikes threaten to disrupt online purchases during Black Friday as retailers try to drum up demand in the face of weak consumer confidence. The walkouts ahead of Christmas also threaten the arrival of festive cards and presents, putting pressure on Royal Mail at its busiest season. 

Royal Mail lost £219 million ($261 million) in the first half through Sept. 25 and has said that a payroll reduction and wholesale changes to deliveries are necessary to cut losses and take advantage of the parcels boom that’s persisted since coronavirus lockdowns. The CWU wants higher pay and an end to what it says are moves for an Uber-style workforce of casual workers and owner-drivers.

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