It appears the city of Portland, Oregon is very serious about Uber operating its ridesharing service illegally, which it's been doing there since last Friday. Today the city announced that it's filed a lawsuit against the company, saying it's in violation of its rules and regulations, and asking for the company to immediately cease and desist its operations there.

"Our main concern is public health and safety, because the state invested in the cities the responsibility to do that," Portland's mayor Charlie Hales said in a statement. "Beyond that, though, is the issue of fairness. Taxi cab companies follow rules on public health and safety. So do hotels and restaurants and construction companies and scores of other service providers. Because everyone agrees: good regulations make for a safer community. Uber disagrees, so we're seeking a court injunction."

In a statement, Uber would not say whether it was continuing operations, but said it "has received a tremendously warm welcome from riders and drivers in and around Portland." The company also noted that it received close to 7,000 signatures from people (though not necessarily Portland residents) to its online petition that asks the city to allow it to run there.

Uber and city officials had been in talks about launching the service there for months, when the company went ahead with the launch last week. City transportation officials responded by threatening steep fines for both drivers and Uber, but not passengers. If caught, fines run $1,500 for the company (for the first offense) and up to $2,250 for the driver. That can climb up to $5,000 for additional violations, making it a potentially wildly expensive endeavor. In a statement, Uber spokesperson Eva Behrend said the company "stands by every driver partner and will fight unjust citations."

Enforcement of those citations was complicated in no small part because of Portland's proximity to neighboring cities where Uber is allowed, including right across the bridge in Vancouver, Washington. Drivers in those places can pick passengers up and drop them off into Portland within minutes, meaning return trips to those areas requires riding without a paid passenger.

As with other instances, officials had concerns about Uber's handling of insurance and background checks from drivers, which are required for city taxi cab drivers. Traditional taxi companies require drivers to have certain rates of commercial insurance and annual background checks, whereas there's been less of a guarantee among transportation startups like Uber and Lyft, that initially ran with lower coverage than some cities required.

Update December 8th, 8:50PM: with comment from Uber.