Ratcheting up a battle with Uber Technologies Inc., London’s government transportation agency is requiring drivers to meet an English-language requirement in order to hold a private-hire taxi license.

The new rules, which apply to UberX and the company’s black car service, come after Uber successfully sued the city to block the introduction of English requirements that would apply only to drivers from non-English speaking countries. The proposal was considered discriminatory. Rather than backing away from the language-proficiency plan, the city is now requiring all drivers to prove their English skills by March 31, 2017.

Uber is facing increased resistance in London, as officials attempt to protect its historic black cab industry, which has been a key part of the city’s transportation system for generations and whose drivers go through intensive training and testing before being approved to drive. Uber drivers, by contrast, face less stringent requirements, and are often less expensive to use.

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London Mayor Sadiq Khan told London’s LBC radio station Tuesday that the language test is one of four conditions he wants to impose on Uber and other private-hire firms. Additional rules include the driver and vehicle identification being made known to customers before their journey, round-the-clock insurance and an advanced driving test.

“If you have a medical issue or you know a quicker route, it’s obvious that the person should be able to understand you,” Khan said of the language test. “Nobody wants private hire vehicles to be extinct. There is a space for them and the black taxi as well.”

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The tussle between the city and Uber shows no signs of going away. Khan said he’s asked the central government to give him “the power to control the numbers of private hire vehicles in London," he said. "I’m hoping having better standards for PHVs, as we call them, will lead to fewer and better ones.”

Uber, which faces resistance to its business from governments throughout Europe, said the rules were unnecessarily burdensome.

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“We’ve always supported spoken English skills, but passing a written English exam has nothing to do with communicating with passengers or getting them safely from A to B," Uber said in a statement. "Thousands of drivers who’ve spent years providing a great service to Londoners will now have to fork out 200 pounds and pass a writing exam, try to find an old GCSE certificate or lose their licence and their livelihood."

To obtain a license, drivers will have to complete a test costing up to 200 pounds ($245) or prove with other documentation they have fluency in English.

"It is essential for public safety that all licensed drivers can communicate in English at an appropriate level," the transportation authority, Transportation for London, said on its website. "Communicating with passengers to discuss a route, or fare, as well as reading, understanding and being able to respond to important regulatory, safety and travel information sent by TfL is crucial to a driver’s role in transporting the public."