Unite the nnion has reiterated calls for the Airbus manufactured Super Puma choppers to remain grounded.
The H225 and AS332 L2 helicopters were banned from flying in the UK after a fatal crash off Norway which killed 13 people.
During investigations into the tragedy, fatigue and surface degradation was discovered in the main gearbox.
It is thought the rupture of a second stage gear “likely” caused the Norway accident but the root cause of the failure is still not fully understood.
In July, the Civil Aviation Authority (CAA) announced plans to lift the ban and a directive stated that “in-house” upgrades must be conducted if Super Pumas are to return to service in the UK.
The European Aviation Safety Agency had previously lifted its ban in October 2016 but authorities in the UK and Norway had kept them grounded until the CAA decision.
Unite regional officer, Tommy Campbell said: “Without all the details being fully known in the Norwegian tragedy Unite believes the decision by Airbus to reintroduce the Super Pumas is not only premature but it potentially jeopardises confidence in the offshore helicopter health and safety system.
“Until a full investigation is complete and the results are fully known the helicopters should not be brought back into usage by commercial operators. Our overriding priority must be the safety of all those working in the North Sea and until we have clarity Unite will not support the reintroduction of the Super Puma H225LP and AS332 L2 helicopters.”