A striking Royal Mail worker has voiced fears up to 25,000 staff could be sacked and new working conditions imposed on those left after the core Christmas season has finished.
The man, who usually delivers letters and parcels in the London area and is being identified as 'Derek' because he wished to remain anonymous, was speaking on the eve of the latest strike which began on Friday.
He said the 115,000 frontline workers were fighting for the very future of the business.
Workers are striking today and further walkouts are scheduled for 11, 14, 15, 23 and 24 December.
Their union, the CWU, has claimed the programme of modernisation the company is seeking, including voluntary Sunday working, in return for a larger pay rise would turn Royal Mail into a "gig economy-style parcel courier, reliant on casual labour".
Royal Mail has argued it is crucial to help it better compete as it places a greater focus on the lucrative parcel delivery sphere at a time when the company is losing £1m a day.
Derek, who is a union member but not a rep, explained that while part of the fight was for better pay, he and his colleagues were walking out to protect the company's values from a future that would mean a worse deal for the public and staff alike.
He said Royal Mail was attempting to weaken its commitments to letter delivery and make its contracted workers go further, through increased flexibility, to line the pockets of shareholders.
Dave Ward, general secretary of the Communication Workers Union, told Sky News even if they were offered a 50% pay rise they would not accept it if the same terms and conditions were attached.
The main gripes, Derek said, covered Sunday working and later start times for deliveries.
"The pay deal is something we wanted but 2% (with more in return for accepting new working practices) was a joke," he said.
"The vision is to start deliveries later and finish later but if you don't complete by your time allocated, we don't know where we stand as the goal posts keep changing. It becomes a conduct issue.
"They've got us by the b****.
"We are cutting off (finishing rounds before completion) on a regular basis because we're not getting paid any extra to clear backlogs."
Derek blamed staff shortages, saying agency workers had been brought in to help.
"We're on £12 an hour. Agency are getting £15-20," he said.
"Freelance drivers are being used to cover vacancies. They (Royal Mail) don't want to recruit.
"The night shifts for Christmas are another issue. The backlog is phenomenal. Packages are being prioritised when the company insists that is not the case.
"It's the terms and conditions that are the paramount issue in this dispute. They're trying to fix something that doesn't need it.
"Once Christmas is over, they'll do whatever they want and impose these changes.
"Compulsory working Sundays - I didn't sign up for that. They say it's voluntary but I'm having to do that now.
"Sickness is going through the roof."
He added that Royal Mail was deducting wages by £117 per day for strike days.
"I only earn £75 per day but they've taken off allowances including for the loss of leaflet drops," he claimed.
"Royal Mail said: "We are not docking extra days' pay - if people work, are on annual leave, off sick or on a rest day, then they are paid as normal; if people take part in strike action, then they are not paid for the period that they are on strike."
Royal Mail reacted to the growing cost of the strikes in October by launching a consultation on job cuts that could see around 10,000 roles cut by the end of August 2023. It later revealed half-year financial losses of £219m.
The company made, what it called, a "best and final" offer to end the dispute in late November.
However, its "extensive improvements" were rejected by the CWU.
A Royal Mail spokesperson said of Derek's comments: "Dave Ward, general secretary of the Communication Workers Union, has made several false statements about job losses designed to mislead and create fear and uncertainty amongst our employees.
"As recently 28 November, we wrote Mr Ward to correct his false allegations that Royal Mail is planning to 'sack' thousands of workers and wants to become 'another courier company'.
"This is simply not true. We have already announced that reductions in 10,000 full time equivalent roles - which have become necessary as a result of industrial action, the need for better productivity and lower parcel volumes following the pandemic - will be achieved through natural attrition, reducing temporary workers and a generous voluntary redundancy scheme which has been oversubscribed.
"We would be happy to look into any concerns the individual has about his pay."