A report by the Civil Aviation Authority (CAA) outlined plans for a veto on helicopters flying during rough seas to reduce the risk of a ditched aircraft capsizing. Helicopters would be grounded during the worst conditions, known as Sea State Six.
The watchdog said the move would make it easier for emergency services to carry out rescues at sea, but there are fears the restrictions - due to start from June 1 - could bring the industry to a standstill.
Jake Molloy, regional organiser for RMT, the UK transport trade union, said it was "cautiously welcoming" the new regulations but warned workers could be left stranded.
He said: "It will have an impact on getting to and from work. I am a wee bit concerned that the CAA have developed the report without thinking through the practicalities.
"Sea State Six refers to average wave heights of four metres. That's extremely common in the North Sea, especially in winter. It wouldn't be surprising if it rules out flights west of Shetland altogether."
Mr Molloy added that the industry had voluntarily attempted bad weather restrictions in the aftermath of the fatal Cormorant Alpha helicopter crash in 1992, but the move had proved "extremely restrictive".
Operators are also expected to fit side floats to offshore helicopter, improve lifejackets and liferafts, and fit hand holds next to push-out windows to make escaping the aircraft easier. The watchdog also demands upgrades to on-board emergency breathing equipment to maximise underwater survival time.
Until these improvements are carried out, offshore workers will be allowed to fly only if they are seated next to an emergency window exit. This will cut the number of passengers able to fly at any one time from about 19 to 13, depending on the aircraft model.
Pilot training and checks will also be overhauled, while the CAA will take on responsibility for inspecting and approving safety standards for each offshore helideck in the UK.
The report was commissioned in the wake of the fatal crash off the coast of Shetland in August, which claimed the lives of four offshore workers. The crash highlighted concerns about the UK's safety record in comparison to countries such as Norway.
Helicopter crashes in Scottish waters have claimed the lives of 38 people since 1997. There have been no deaths in Norwegian territory.
Jim McAuslan, general secretary of pilots' union Balpa, said: "The CAA has recognised that independently setting and protecting decent helicopter flight safety standards in the North Sea is more effective than a 'light touch' approach.
"Pilots particularly welcome the ban on flying in adverse conditions and the recommendations on how the chances of surviving an incident can be improved."
The report comes as a Fatal Accident Inquiry continues into a Super Puma crash in the North Sea in April 2009, which killed all 16 on board.
Robert Paterson, health and safety director for Oil & Gas UK, said the CAA review had "found no significant differences between UK and Norway operations".