Postal services in Derry were suspended today after a threat was made against a member of staff last night.
Workers at the sorting office in Great James Street in the city will hold an emergency meeting on Monday morning to discuss the threat.
Services were suspended earlier this year when threats were made against other members of staff in the loyalist Waterside area of the city.
They were purported to be made by the loyalist Ulster Defence Association, which subsequently denied involvement.
Postal services throughout the Province were also suspended earlier this year in protest at the murder of Catholic postman Daniel McColgan by the Ulster Freedom Fighters.
Earlier this week the Red Hand Defenders, a cover name for the UDA/UFF, warned it would take "military action" after civilian construction worker David Caldwell was killed by a booby trap device at a Territorial Army camp in Derry.
Security sources have blamed the Real IRA for planting the device, believed to have been contained in a lunchbox.
Five people, four men and a woman, are still being questioned about the killing.
Charlie Kelly from the Communications Workers Union said postal staff were taking the latest threats seriously.
"Staff are very, very worried, particularly in light of events this week. "Because they are out on the street in the morning, they are in the front line, they see themselves as easy targets."
Mr Kelly said he hoped services could resume on Monday but added that the safety of staff was of paramount importance.
PA