Postal workers in the greater Belfast area are to stage a 24-hour stoppage in protest at the murder of colleague Danny McColgan.
The decision was announced after union representatives met Northern Ireland Secretary John Reid at Hillsborough Castle today.
Up to 2,000 workers will be involved in the stoppage when Mr McColgan's funeral takes place tomorrow.
All deliveries were suspended today.
John Keggie, deputy general secretary of the Communication Workers Union, said staff were outraged by the murder and the threat against other public sector workers.
He said: "We will consider further options if the threat is not removed and this could affect postal services for a lengthy period.
"We have to discuss that possibility but we are not having our members indiscriminately murdered."
Earlier Sinn Fein president, Gerry Adams, claimed the Government was not doing enough to confront loyalist paramilitaries involved in the north Belfast terror campaign.
It was up to the Government to prove to nationalists and republicans that it was taking appropriate action.
Mr Adams said: "There is a marked reluctance to face up to the UDA because there is a different attitude to violence when it comes from loyalists and because many of those involved in that organisation are in the pay of the British Government."
* A cowardly minority of Loyalist Paramilitaries are waging a war against the weak, the vulnerable and most exposed people in Northern Ireland, Secretary of State John Reid said today.