The NUJ has called on the Chief Constable of the PSNI, Sir Hugh Orde, to hand over the investigation into the murder of Sunday World journalist Martin O'Hagan to an outside police force.
In a statement to mark the fourth anniversary of the murder of Mr O'Hagan, the union called for "an acceleration of the investigation into the killing". It also condemned the ongoing campaign against the Sunday World.
It also warned that journalism in Northern Ireland is under threat with the upsurge in street violence and divisions within loyalism.
Mr O'Hagan was shot dead by a gunman as he and his wife Marie walked home from a night out in a local pub in Lurgan on September 28th, 2001.
The shots were fired from a passing car, which drove away at high speed.
Calling for the involvement of an outside force in the investigation, NUJ Irish secretary Séamus Dooley said that rumours linking police informers to the death of Martin O'Hagan raised fundamental questions about the murder.
Mr Dooley said: "In our discussions with the PSNI we have been advised that the police do not have sufficient evidence to bring charges against the suspects.
"We naturally accept that charges can only be brought on foot of strong evidence. There is also a strong belief that the police know who killed Martin O'Hagan.
"Throughout Northern Ireland there is a deep suspicion that some of those linked to the murder have had an association with the police and army and are in some way protected from prosecution. The only way this matter can be resolved is for the Chief Constable of the PSNI to hand over the investigation to an outside body.
"At the very least the O'Hagan murder must be put on the cold-case list and given priority as one of the many unsolved murders in the North."
Mr Dooley condemned the campaign against the Sunday World by loyalist groups and paid tribute to editor Jim McDowell and the journalists at the Belfast office who, Mr Dooley said, had stood firm in the face of intimidation.
"This latest intimidation against the paper and against newsagents is another blow to democracy in Northern Ireland. The decision to target media workers is extremely sinister. The campaign against newsagents has been terrifying," Mr Dooley said.
Stacks of the newspaper have been set alight inside shops, shopkeepers have been threatened and at least one shop owner was told he would be shot if he continued to sell the paper.
Van drivers have been threatened and vehicles hijacked. This action by the UDA strikes at the heart of democracy and represents an assault on the right to freedom of expression."
Mr Dooley added: "Against this backdrop, the NUJ is concerned at the decision of the PSNI to request journalists and photographers to hand over information relating to recent street violence, including photographic footage. The NUJ is advising members not to co-operate with this request.
"The role of journalists is not to act as agents of the security forces. Journalists covering street violence are already at risk. If those responsible for instigating street violence believed the media were going to co-operate with the security forces, reporters and camera crews would be under even greater threat."
NUJ president Tim Lezard called on employers to give priority to the safety of journalists who are covering street violence.
"It is essential that the health and welfare of journalists is not put at risk.. Journalists should not be required to operate alone in risky situations and risk assessments must be constantly undertaken," Mr Lezard said.