Sorting office workers have blamed the problems on the UK postal service's dedicated temporary staff recruiter, Angard Staffing Solutions, accusing the agency of mishandling payments for work over the holiday period.
Many workers, who complained to the Guardian newspaper, claim their hours were logged incorrectly and in some cases the amounts paid per hour were not the agreed terms that workers had initially signed up to when taking the work. Angard had advertised the Christmas rate at £5.95 per hour.
An independent online chat forum, Royal Mail Chat, set up for postal employees to vent their frustrations, has received dozens of comments from irate workers waiting to receive their money.
One post said: "Been sent a letter saying I actually owe Angard money, when actually they owe me over twice as much. Except...they got confused about who they really are and asked me to send a cheque payable to Royal Mail. Of course, my hours are quoted entirely wrongly on the letter."
Another post said: "I am giving them until the end of the week, then filling in ET1 form. Had enough."
A Communication Workers Union (CWU) spokeswoman said: "This has been a complete mess and very distressing for many of the workers. We have examples of people working in the same office and one was paid, while the other wasn't.
"We are aware some people may be seeking a legal route but we are trying to resolve this dispute with Royal Mail as quickly as possible."
Angard was overwhelmed by applications before Christmas, the company said, when it received over 100,000 applications for the 20,000 jobs advertised.
Royal Mail's managing director for operations and modernisation Mark Higson wrote to temporary recruits earlier this month thanking staff but admitting there had been issues surrounding payments.
A Royal Mail spokesman said: "It was acknowledged in Mr Higson's letter that while the large majority of temporary employees were paid correctly on time, Royal Mail was keenly aware that for some people, there were delays and difficulties with their pay. Royal Mail has apologised for this and worked very hard to resolve any outstanding problems."
The spokesman added that three additional letters had been sent to casual workers explaining the hours worked and pay earned. "To the best of our knowledge, any outstanding pay has now been paid," he said.