Uber’s post-IPO woes continued Monday when the ride-hail giant was stripped of its license to operate in London over its failure to ensure passenger safety.

The potential loss of one of its largest markets — which represents close to 4 percent of its business — sent the stock tumbling more than 6 percent in intraday trading.

Transport for London, which oversees the UK capital’s transportation system, deemed the ride-hailing giant “not fit and proper” to hold a license, saying it has not done enough to stop unlicensed and uninsured drivers from carrying riders.

“Safety is our absolute top priority,” Helen Chapman, the agency’s director of licensing, regulation and charging, said in a statement. “While we recognize Uber has made improvements, it is unacceptable that Uber has allowed passengers to get into minicabs with drivers who are potentially unlicensed and uninsured.”

The decision — which came the same day Uber’s existing license was set to expire — will not immediately pull the company’s cars off London’s streets. Uber said it will appeal the move, which it called “extraordinary and wrong.”

“On behalf of the 3.5 million riders and 45,000 licensed drivers who depend on Uber in London, we will continue to operate as normal and will do everything we can to work with TfL to resolve this situation,” Jamie Heywood, Uber’s regional general manager, said in a statement.

Still, it’s the latest blow for the money-losing company since its May stock listing when investors sent the stock down 8 percent — marking the worst IPO for a marquee name in at least a decade. The former Silicon Valley darling’s stock has lost one-third of its value since the IPO has it burns through billions a year cutting prices to compete with Lyft and other rivals.

Wedbush analyst Dan Ives called Monday’s ruling “a major black eye” for Uber, saying the London action raises concerns that Uber’s business could be in trouble in other cities and countries if the London ruling doesn’t go its way.

“This is a moment of truth for Uber and Dara as they continue to significantly be in the crosshairs of regulators both in the US as well as in the UK,” Ives said. “It continues to be a horror show with Uber’s inability to handhold regulators through these issues.”

The London move follows New York City’s crackdown on the ride-hailing industry, including a freeze on most new for-hire vehicles that was extended in August after Uber sued over the policy. The city has also imposed a pay floor for ride-hail drivers that drew an unsuccessful legal challenge from Lyft.

Uber and other “gig economy” company are also being threatened in California, where state legislators want to require companies to classify their workers are employees rather than contractors, which will result in workers getting sick days and workers compensation.

Transport for London officials say unauthorized drivers were able to upload their own photos to other drivers’ accounts, allowing them to pick up passengers posing as the real driver.

That happened on at least 14,000 trips — all of which were uninsured and some of which were taken by unlicensed drivers, one of whom had their license previously revoked, the transport agency said.

Shares of Uber are down nearly 30 percent since its IPO in early May, with the stock closing down 1.3 percent Monday to $29.18.