A tribunal is set to rule in a test case on the employment rights of drivers at private hire firm Uber which could affect thousands of other workers.
The GMB union has taken two test claims, arguing that Uber drivers should be entitled to holiday pay, a guaranteed minimum wage and breaks.
The union said the outcome of the Central London Employment Tribunal case could have "major" implications for more than 30,000 drivers across England and Wales as well as other workers.
The case centres on whether the drivers are self employed.
Uber designates its drivers as self-employed rather than employed workers, and claims it is a technology company rather than a taxi firm.
The taxi app company says it allows people to be their own boss and work flexibly, but it faces a legal challenge from drivers who say it is acting unlawfully.
The test cases, brought by drivers James Farrar and Yaseen Aslam, argue they should be entitled to holiday pay and receive at least the national minimum wage.
But the taxi firm's representatives say its drivers have a choice about their work and argue there is nothing to force them to work exclusively for Uber, giving them freedom to work with other private hire operators.
Uber, which has its headquarters in the Netherlands, has previously argued that UK drivers should not be allowed to enforce UK employment rights in UK courts, and should only seek arbitration in the Dutch courts.
Maria Ludkin, legal director at the GMB said: "This case represents the first proper legal review of whether jobs in this part of the so called gig economy really represent a new paradigm of freedom and self employment, or in fact are simply a new technology ploy to deny employed workers ordinary employment rights and a national minimum wage."