A leading trade union is taking another legal case to challenge the status of workers classed as self-employed.
The GMB is bringing a test case on behalf of three drivers at taxi firm Addison Lee, arguing they are "workers" and so should receive benefits such as holiday pay.
The union won a similar case against taxi hailing firm Uber last year, although the company is appealing against the decision.
Maria Ludkin, the GMB's legal director, said: "Addison Lee drivers work for Addison Lee and are entitled to the same basic rights and benefits as workers in other industries.
"GMB continues to fight for the rights of our members wherever we see exploitation disguised as bogus self-employment."
Liana Wood, of law firm Leigh Day, who will represent the drivers at a Central London employment tribunal starting on Tuesday, said: "On behalf of our clients we will claim that Addison Lee is wrongly classifying its drivers as self-employed with the result that drivers are denied the rights and protections that they were lawfully intended to have, including the right to not have their contracts terminated because they are members of a trade union."