The battle for rights for gig economy workers is stepping up as the union behind legal action against Uber targets three taxi firms that say their drivers are not entitled to holiday pay or the minimum wage.

Green Tomato Cars, which calls itself “London’s green and ethical car service”, luxury airport transfer specialist Blacklane and Birmingham’s A2B are facing claims from former drivers who say they are “workers” and not independent contractors as the car firms insist.

The cases are backed by the Independent Workers Union of Great Britain (IWGB) union, which has won a string of successful cases on worker status, including against Uber. The ride-hailing app is to challenge the ruling at the court of appeal.

An employment tribunal test case backed by the GMB union also found that some Addison Lee drivers had been wrongly classed as self-employed. Addison Lee has been granted the right to appeal against the case.

“The bogus classification of private hire drivers as independent contractors in order to deprive them of employment rights is rampant across the sector. It’s not just Uber and Addison Lee,” Jason Moyer-Lee, the general secretary of the IWGB, said.

Nelson Salei, a former driver for Green Tomato, says he is a worker and so is entitled to be reimbursed unpaid holiday pay.

Salei worked for the private hire group for several months last year, usually on five-day rolling contracts. He left after claiming he was not paid for several days of a contract after a dispute over a fare that was booked but did not turn up. He said the non-payment just before Christmas “was really frustrating”. “I wanted to have a comfortable Christmas but I had to ask people to lend me money,” he said.

Salei earned £20 an hour on the contract, under which he promised to work only for Green Tomato and turn down work from other companies such as Uber, but estimates that he took home less than half of that after paying for petrol, insurance, maintenance and leasing his car. He says he never asked for holiday pay. “I didn’t know much about my rights,” he said.

Green Tomato Cars said it “prides itself on being an ethical company and, in particular, in our relationship with drivers”.

“We have discussed the situation with Mr Salei and his union representative through the Acas mediation process, and maintain our position that there are no grounds for his claim,” it added.

“We will of course comply with the requirements of the tribunal, where we expect to successfully defend the claim.”

Mariusz Jakubowski, who worked for Blacklane in Glasgow, until just before Christmas last year, said he didn’t receive a set rate for jobs. The app works by offering a rate for a job in a particular area that gradually increases until a driver takes it up.

Jakubowski left after he was fined by the company when a customer complained he handed them a personal business card, something he denies doing. He said he had rented out his car and stopped private-hire driving after leaving Blacklane. “I was earning good money,” he said. But after receiving the fine and being assaulted by a passenger while working for another taxi service he said: “I realised it wasn’t worth it.”

Berlin-based Blacklane, which operates in more than 250 cities around the world and is partly backed by the carmaker Daimler, said: “We have not received any official information, documentation or filings about this case. Therefore, we cannot comment in any meaningful way.”

A2B’s owner Veezu, which owns several private hire firms, did not respond to a request for comment.

The gig economy has proved to be a battleground for disputes about employment status involving firms such as takeaway company Deliveroo and courier firm CitySprint. Its emergence also prompted a full-blown government review into modern employment practices, led by Matthew Taylor, a former adviser to Tony Blair.

Bogus self-employment is thought to deny basic rights to about 1.1 million couriers, minicab drivers and other workers.

Moyer-Lee said that the government had been slow to act on the prime minister’s promise to help workers and offered little in concrete action in response to the Taylor review. He called for better enforcement of employment rules.

“What we’ve seen in case after case is that the tribunal finds these people are workers, often in scathing terms, and that shows we’ve got a serious problem in enforcement of the law,” he said.