Months after Uber Technologies Inc. won a reprieve in a high-stakes battle over its operations in the U.K. capital, a decision to grant its London license is in question. United Cabbies Group, which represents the city’s taxi drivers, brought a legal challenge Wednesday over the June decision by judge Emma Arbuthnot that granted Uber a 15-month probationary license, after London’s transit authority revoked its earlier permit, citing safety concerns. Arbuthnot’s decision was based on “wholly unsatisfactory reasoning,” the group’s lawyer, Robert Griffiths, said in court. Her ruling was also “tainted by actual or apparent bias,” the group said in its filings for the hearing. That’s because Arbuthnot decided in August, soon after making her original determination, not to hear a further case involving Uber. Her decision followed a newspaper report that her husband worked for a strategy firm that has advised the Qatar Investment Authority, one of Uber’s investors, the group said. The bias claim is “extremely tenuous” and at the time of the hearing, Arbuthnot didn’t know her husband had advised the QIA and wasn’t aware of any link between Uber and the QIA, Uber said in its filings for the case. The cab drivers’ challenge “lacks common sense,” it said.Uber has introduced new safety features for riders and better protections for drivers since the June court ruling, including emergency assistance, a spokeswoman said. Representatives for UGC didn’t immediately comment. Black cab drivers, who drive the city’s famous Hackney carriages and spend years studying for the London transport regulator’s tough “knowledge” tests — which require extensive recall of the city’s road network — have been hurt by the proliferation of Uber drivers and have pushed for tighter regulation. London is one of the ride-hailing giant’s most lucrative markets, and Uber needs a license in order to operate there. The company’s previous private hire permit lasted five years.