Union leaders have won the first round of a battle for holiday pay under a European directive limiting weekly working time.
Union leaders want paid holidays for offshore staff
Employers in the oil and gas industry argue that the working time regulations have no jurisdiction offshore.
Unions believe a tribunal which has ruled that cases can be heard could pave the way for four weeks paid holidays for more than 20,000 workers.
The oil industry is studying the ruling and further challenges are likely.
The working time directive is aimed at limiting the average working time for employees in the European Union to 48 hours a week.
A preliminary hearing covering 300 workers was held at the Employment Tribunals Service in Aberdeen.
It concluded that the laws do apply to installations outside British territorial waters.
The ruling means workers will be given the chance to have their cases heard at employment tribunals.
The OILC union, which represents 120 of the employees, said it was "delighted" with the news, but warned there was still a long way to go, as employers now have the right to an appeal.
Jake Molloy of the OILC said: "The judgement has ruled that the regulations apply to offshore work in the UK sector of the Continental Shelf.
"We are delighted, but this is the first battle in what could be a long and drawn out war.
"The decision could be appealed and this could go to the employment service, the House of Lords and subsequently to Europe.
"As we have said from the outset, there is no doubt that the regulations apply offshore and to our favour. This decision today makes us supremely confident that this will be found at all stages."
Graeme Tran of the Amicus union said he was delighted with the decision.
Mr Tran said: "I do believe the employers are playing delayed tactics but I look forward to the debate over the holiday entitlement."
He added that Amicus was still prepared to have 11th-hour constructive talks with contractors over holiday leave.
Frank Doran, Aberdeen North Labour MP, said the ruling was an important decision.
Mr Doran added: "It also opens the way to the oil industry and the trade unions to sit round the table and resolve the long-standing issue of holiday entitlement for offshore workers.
"I have been working with Gerry Sutcliffe, the employment minister in Westminster, the trades unions and the oil industry and I have no doubt that there is a strong desire to reach an agreement now that the major legal obstacle has been removed."