A loading platform grazed the Boeing's door on Sunday but was not reported by the ground handling agent Air Terminal Services (ATS).
The airline only became aware of the damage after the aircraft returned to Auckland and routine inspections were made.
Fiji Trades Union Congress national secretary Felix Anthony said the incident highlighted concerns around security at the airport and the safety of passengers.
"We have unqualified people who are performing duties that they really should not be performing," he said.
"Nadi is a place where accidents are waiting to happen."
Mr Anthony said around 200 ATS staff remain locked out of work since attending a shareholders' meeting on 16 December.
ATS management said "temporary" staff have been filling the void.
Air New Zealand said damage to the aircraft was minor and did not compromise safety.
It said the 342-seat aircraft was repaired on arrival in Auckland and returned to service.
ATS chief executive Hare Mani, has said previously that it is completely safe to travel to Fiji through Nadi airport.
Nadi airport workers permitted to protest
Meanwhile, Mr Anthony said it was surprising the right to protest in Fiji was being observed by the police.
Mr Anthony said a march has been planned on Saturday in Nadi to support locked out workers and shareholders.
He said the right to protest was written into Fiji's constitution and a permit was issued on Wednesday by police in Lautoka.
Mr Anthony said the marchers will protest the conduct of management at ATS.
"And also to call upon government to act on this matter without bias and attempt to address the issues that gave rise to the crisis that is taking place at the airport in Nadi."