Thousands of letters went undelivered in Preston after a row between a postman and his boss saw a walk-out at a postal delivery office.
Workers at the Royal Mail site on Christian Road in the city centre walked out yesterday morning after the argument led to a worker being suspended pending an investigation.
However, 150 workers were left furious after the manager involved in the argument was not suspended in the same way.
A crisis meeting is due to be held at the site on Saturday morning in an attempt to break the deadlock and get letters delivered again over the weekend.
Lenny Crook, a representative for the Communication Workers’ Union (CWU), said: “Our members asked for parity of treatment between our member and the manager involved and the business has refused this request, which started the walk out.
“The management then refused to discuss the situation with workers until they went back to work, and the workers refused to go back to work until the manager was suspended.
“There will be a further meeting on Saturday morning in an effort to resolve the situation, although I would imagine it is unlikely there will be a resolution.”
A Royal Mail spokesman described the incident as “unlawful industrial action” and confirmed it had impacted deliveries in the PR1, PR2, PR3,PR4 and PR11 postal areas.
Delivery director Adrian Fielding said additional staff and managers had been drafted in yesterday to attempt to deliver mail and limit the impact of the action.
He said: “We are fully aware of the concerns of staff which relates to a conduct case involving one individual in the office and Royal Mail has robust procedures, agreed with the CWU, to deal with such matters.
“This needs to be resolved within the standard disagreement framework as agreed by the Union and implemented successfully elsewhere.”
He added that deliveries had been prioritised to Royal Mail’s tracked mail services, including Special Delivery items, and asked people not to visit the Christian Road site unless they had received a card asking them to do so.
Mr Fielding said: “We sincerely apologise again to our customers for the impact of this unlawful industrial action and we will keep them informed of developments.”