When Uber first arrived on the scene, it rapidly overtook the market in the United States. Young and old, rich and poor—seemingly every American was enchanted by the speed and convenience that the ride-sharing mobile app offered them. A nationwide empire was quickly born. Now, though, we’re starting to see that conquering the rest of the world could be more difficult.

The New York Times reported that in London, a crucial court case is underway that could largely shape Uber’s international future. The British capital’s regulators made a decision earlier this year to revoke Uber’s local operating license; Uber is now appealing that decision.

Not only will the case decide whether Uber has access to a market of 8.8 million potential customers, but it will also set a key legal precedent that could impact the company’s expansion to other global cities. Additionally, the case will be a major test for Dara Khosrowshahi, the new chief executive at Uber, who’s been on the job just 10 months so far. 

“The trial is one of the first big tests of Khosrowshahi’s leadership of the company and new approach,” University of London professor Andre Spicer said. “The judgment will show whether authorities are willing to accept Uber with some of the harder edges knocked off, or whether there are more fundamental questions about the Uber model.”

London will be a key battleground as Uber fights for its future. It’s the company’s biggest market in Europe (there are 3.6 million people in the city who ride an Uber at least once every three months, and 45,000 drivers transporting them). Going without that business would hurt. On top of that, losing this case would be biggest regulatory setback in Uber’s young history, and it might portend a slowdown for Uber’s future plans such as expansion in Asia and a possible initial public offering. 

For Khosrowshahi, these are turbulent times. Not only is the London case weighing on him heavily, but he also has to deal with government investigations, management turnover issues, data security threats, and allegations of a sexist company culture that arose late last year as part of the #MeToo movement.