Angry agency staff stormed out of the main Royal Mail sorting office in Birmingham in a dispute after their Christmas wages went unpaid.
Up to 35 workers led an hour-long wildcat protest at the Newtown centre when their weekly pay failed to materialise with Christmas drawing ever closer.
The postal giant subsequently issued an apology to unpaid workers – and said it had overpaid some casuals to ease the difficulties.
But agency worker Royston Allcock, 34, said: “There are some agency workers here who have not been paid for three weeks. They are all workers who have been employed by the Royal Mail especially for the Christmas period.
“Some of us still do not know when we are going to get paid. We should get our money on a weekly basis every Friday. This is my third week without wages.
“I have a wife and four children and I was relying on the money to buy presents, do some Christmas shopping and going out over Christmas.
“A lot of young people here may now not have any money over Christmas. People have done the work and need the money.”
Royal Mail spokesman Heulyn Davies said: “Difficulties with the payroll system meant some temporary workers regrettably were not paid on time or by the correct amount last week.
“We apologise for this as our temporary Christmas staff are very important to us. Firm action is being taken to resolve outstanding pay issues as soon as possible.
“The vast majority of our Christmas temporary recruits have been paid as usual into their bank accounts. Where this was not possible, we have made huge efforts to put in place additional payment channels.
“This involves staff receiving a voucher which can then be redeemed for the relevant amount of cash at any Post Office branch. In some cases, we have overpaid people in order to expedite payments. We will, of course, be making appropriate adjustments in future payments.
“We apologise for the difficulties that this situation has caused to a minority of temporary workers.”