Union leaders are going to court to test whether the Working Time Directive can be applied to offshore workers.
Thousands of oil workers could be affected by the outcome of five days of preliminary hearings in Aberdeen.
Central to the union’s argument is a claim for workers to receive four weeks’ paid holidays. However, the oil companies disagree and say the directive has no jurisdiction offshore.
If the hearing determines that it does apply offshore, it could clear the way for hundreds of oil workers to take their case for paid holidays to court.
Jake Molloy, general secretary of the offshore union the OILC, said: “This is very crucial because after all this is a health and safety directive.
“We are trying to reduce the annual hours, give the guys a better work/life balance approach and for the increasing female working population the same issues apply.”
Last week members of the European Parliament voted to remove the UK’s individual opt-out.