Uber’s stance has always been that it’s a software company. Uber connects people wanting a ride to those offering a ride. It’s a logistics company. Uber simply connects third-party contractors with customers. Its drivers are independent contractors, not employees.

That notion is being challenged quite a bit as of late, and it looks like Uber is facing another lawsuit over the question of employee or contractor.

UK union GMB, which represents professional drivers, has engaged a law firm to file suit against Uber “on the grounds that Uber is in breach of a legal duty to provide them with basic rights on pay, holidays, health and safety and on discipline and grievances.”

According to GMB, Uber drivers are employees and the company should conform to all applicable employment laws.

“The Uber assertion that drivers are ‘partners’ who are not entitled to rights at work normally afforded to workers is being contested,” says Nigel Mackay,a lawyer involved in the suit. “Uber not only pays the drivers but it also effectively controls how much passengers are charged and requires drivers to follow particular routes. As well as this, it uses a ratings system to assess drivers’ performance. We believe that it’s clear from the way Uber operates that it owes the same responsibilities towards its drivers as any other employer does to its workers.”

GMB demands that Uber adopt the national minimum wage, give paid holidays, ensure that drivers take rest breaks and have a maximum work week, and “adhere to legal standards on discipline and grievances.”

“A successful legal action against Uber could see substantial pay outs for drivers, including compensation for past failures by the company to make appropriate payments to who we argue are their workers.” Mackay adds.

Last month, the California Labor Commission ruled that an Uber driver was an actual employee – as Uber is “involved in every aspect of the operation.”

But Uber’s argument is that its setup lets drivers choose everything.

“One of the main reasons drivers use Uber is because they love being their own boss,” a spokesperson for Uber told Engadget. “As employees, drivers would drive set shifts, earn a fixed hourly wage, and lose the ability to drive elsewhere. The reality is that drivers use Uber on their own terms: they control their use of the app.”

That lawsuit only applied to one woman, however, and didn’t result in any sort of mandate. GMB thinks that this new lawsuit could have farther reaching consequences.

In other Uber news, the company is likely populating its in-app maps with ghost cars.