Offshore workers are being urged to opt back into regulations aimed at limiting the working week to 48 hours.
The Rail, Maritime and Transport (RMT) union said any potential job losses could be minimised if staff were covered by the Working Time Directive.
Union members are to be balloted on industrial action over issues including shifts, sick pay and jobs amid the slump in oil prices.
RMT general secretary Mick Cash said: “RMT is urging offshore members to opt back in to the provisions of the Working Time Directive as that move will seriously hamper efforts by the employers to impose shift patterns which would wreck the work-life balance of staff who already spend prolonged periods away from home.
“The attack on jobs and working conditions in Britain’s offshore industry is as sharp now as it was at the bottom of the oil price slump and RMT believes that companies are exploiting the situation to launch an unprecedented assault on the workforce and the imposition of the new shift patters is central to that.
“The preparations for ballots are in hand and RMT will work with sister unions in the coming months to stave off this attempt to hammer down on the workforce across the offshore industry.”