The Fire Brigades Union has called for heads to roll following a botched internal recruitment drive.
Union bosses said frontline firefighters have been left frustrated and angry by errors made at headquarters.
The Northern Ireland Fire & Rescue Service (NIFRS) has admitted that eight firefighters were wrongly told their bids to be considered for station commander posts were successful.
The admission comes just three years after another error during which an outsourced company employed by the service tallied candidate scores wrong.
The latest mistake has occurred at a time when NIFRS is already being investigated over recruitment practices.
Fire Brigades Union vice-president Jim Barbour said: “We have been waiting on this round of promotions for a considerable time and firefighters are frustrated as they see constant mistakes being made at headquarters — mistake after mistake.
“This is going back two, three, four years for firefighters. They are extremely frustrated and angry and there is a lack of confidence in the processes now. That is completely understandable.”
It is understood candidates for the station commander posts were put through tests before being informed of the decision by letter in the past few weeks. However, some letters wrongly told staff they had been successful and a second round of letters had to be issued after this was discovered.
“These people have been waiting on this for months, and for erroneous letters to be issued smacks of complete and utter incompetence,” Mr Barbour said.
The Fire & Rescue Service on Monday confirmed that at the request of Department of Health, Social Services and Public Safety, two independent reviews are being carried out by internal auditors at Department for Agriculture and Rural Development and by London Fire Brigade into NIFRS’s whole-time firefighter recruitment process.
Mr Barbour said: “We have lost confidence in internal procedures. Headquarters will be aware of the external investigations and to make another mistake at this time, quite frankly, heads should roll.”
A spokeswoman for the Northern Ireland Fire & Rescue Service confirmed on Monday that “eight members of staff did recently receive a letter relating to the annual selection cycle for station commander posts”.
“Unfortunately due to an administrative error these eight members of staff were incorrectly identified as being successful for consideration for station commander posts,” she said.
“As soon as this mistake was detected, we issued a letter immediately to the eight members of staff sincerely apologising for this human error.”
The spokeswoman also confirmed that there was a previous issue in which an “administrative error” was made in 2009 by “an external provider of Assessment Development Centres (part of our recruitment and selection process) and not by NIFRS itself”.
She said: “Deloitte, the external provider, acknowledged full responsibility and regret for the administrative error in the sorting of the final scores in a Assessment Development Centre held in May/ June 2009 and which was then used for two tranches of internal promotion within NIFRS in January 2010 and September 2010.
“We sought legal advice and this issue, which affected a small number of operational staff, has been rectified and resolved with Deloitte. The NIFRS contract with Deloitte for the provision of Assessment Development Centres ceased on June 30, 2009.”