Uber has launched legal action against Transport for London over new rules for private hire companies which are designed to improve passenger safety.
The car hire app is questioning the legality of several new rules - including one which will compel drivers from non-English speaking countries to pass a two-hour written test.
Although Uber says communication skills are important, it claims the test in question is too difficult and goes beyond the requirements for British citizenship - so much so that 7% of the UK population would fail the exam.
It also warns that tougher rules on commercial insurance, which would require drivers to have a policy even if they are using their vehicle for personal reasons, could leave part-time drivers worse off to the tune of £350 a year on average.
Uber is also challenging TfL's demand to launch a call centre in central London by October, and argues its existing customer support provisions are sufficient.
It further claims that new measures which mean it will have to notify TfL of changes to the Uber app in advance will harm innovation and slow the roll-out of new features.
Tom Elvidge, Uber's general manager in London, said: "This legal action is very much a last resort. The goalposts have moved at the last minute and new rules are being introduced that will be bad for both drivers and tech companies like Uber."
However, other private hire companies have criticised Uber for launching the legal challenge - including Addison Lee, which said the whole industry was involved in the consultation which led up to the new regulations.
Transport for London says it will defend its proposals in court.
"These have been introduced to enhance public safety when using private hire services and we are determined to create a vibrant taxi and private hire market with space for all providers to flourish," a spokesman added.
The consultation was launched following months of protests by black cab drivers who feel apps such as Uber are damaging their livelihoods.
Back in January, TfL dropped a proposal to impose a five-minute wait time for customers who use car hailing apps.