Daniel McColgan: Postman was shot as he arrived for work in January

Employees at the Derry sorting office are meeting on Friday morning to decide how to react to the threat.

Staff in the city have already gone on strike twice this year.

Mail deliveries in the city were disrupted when workers walked out earlier this month after a Catholic postman was warned to stay out of the Waterside area.

However, Consignia, the company that runs Royal Mail, later said it had confirmation from paramilitary sources that there was no threat to Catholic workers.

Management read out a statement from the loyalist Ulster Defence Association (UDA)which said it did not make the threat.

Murder

That threat came just three weeks after postal workers walked out in protest at the UDA murder of Catholic postman Daniel McColgan near Belfast, and also threats made to Catholic postal workers.

Workers returned to work after receiving a police assessment of a threat issued by the UDA using the cover name Red Hand Defenders.

The UDA initially used the cover name when admitting it had murdered Mr McColgan as he arrived for work in Newtownabbey on 12 January.

But it later admitted the murder, and four days after the killing ordered the Red Hand Defenders - the name being used by an element in its own ranks - to stand down.

Postal deliveries were suspended for two days following Mr McColgan's murder and rallies were held across the province in protest at the threats.