A UK window salesman who did not receive a paid holiday for 13 years has been backed at the European Court of Justice in his landmark legal battle.
Conley King worked for a sash window firm on a self-employed basis, but was later found to have workers' rights.
In a closely-watched case, the EU court ruled Mr King was also entitled to his untaken leave at the company.
Legal analysts said the decision could have significant implications for firms in the so-called gig economy.
Mr King worked as a commission-based salesman for The Sash Window Workshop between 1999 and 2012.
After he was dismissed from the firm, a UK tribunal ruled that Mr King should have been classified as a worker.
He also brought a claim for £27,000 of holiday pay he says he should have received.
The Sash Window Workshop said Mr King worked "as a self-employed salesman under an arrangement that suited him".
"We would like to reiterate that at no point was he prevented by us from taking any time off for holiday or otherwise, as there was no requirement for him to request it or for us to agree to it," the company said.
The case now returns to the UK Court of Appeal for a further ruling.
The European court was asked to decide whether EU law allowed him to claim payment for the entire length of his employment.
It decided there was no time limit for his claim, a decision which lawyers said opens the door for similar cases.
"An employer that does not allow a worker to exercise his right to paid annual leave must bear the consequences," the court ruled.
Legal experts said the decision meant companies which routinely use staff on self-employed contracts - such as taxi or delivery firms - could face potentially huge liabilities if that status is later challenged.
James Williams, the barrister who represented Mr King, said it left employers who have miscategorised workers as self-employed, liable for back holiday pay when the workers' employment is terminated.
The head of the IWGB trade union, Dr Moyer-Lee, said the "bombshell judgement" was a "game changer for the so-called 'gig economy'".
"The law is now recognising the massive unpaid debt of 'gig economy' companies to their workers and IWGB members will be coming to collect."
What is the gig economy?
In the gig economy, instead of a regular wage, workers get paid for the "gigs" they do, such as a food delivery or a car journey.
In the UK, it is estimated that one million people are employed in this type of capacity.
Jobs include couriers, ride-hailing drivers and video producers.
Workers in the gig economy are classed as independent contractors.
That means they have no protection against unfair dismissal, no right to redundancy payments, and no right to receive the national minimum wage, paid holiday or sickness pay.