The landmark case in Sweden saw the Stockholmer fined 2,500 kronor ($299) for "driving taxi goers without permission and without taxi driving legitimation", reported the Transportarbetaren union publication.
"This confirms our understanding that UberPop is nothing more than an organized black market taxi service," Markus Petterson, the secretary of the Swedish Transport Workers union Transports förbund, told the paper.
The controversial initiative has already been banned in several European countries including France and Germany, although some drivers are continuing to offer the technically illegal service. A study earlier this year by Sveriges Radio suggested that three out of ten UberPOP drivers in Sweden have not been paying taxes.
The car-sharing service, which is currently active in 60 countries, launched in the Swedish capital in early 2013 and also operates in Gothenburg.
Earlier this year its founder Travis Kalanick said the system was set to create 50,000 new jobs in Europe in 2015, and would help take 400,000 cars off the road by encouraging drivers to use shared rides instead.
The firm has recently been valued at nearly 40 billion dollars.
The car-sharing service Uber faced questions this summer about how closely it vets drivers after a Swedish newspaper reporter managed to enroll with the company without being given any training.