The PUC's vote on Thursday reduced the fine from the $49.9 million that administrative law judges had recommended last year. The PUC had accused the ride-hailing service of operating without a PUC license from February to August 2014.
The PUC reduced the fine because Uber has modified its internal practices to comply with the commission's conditions. The company has not had significant compliance problems since the PUC granted it authority to operate, Commissioner John Coleman Jr. said in a statement.
The final fine is "necessary to deter Uber" and other companies from future violations, Coleman said.
Uber said it was shocked at the size of the fine after competitor Lyft paid a $250,000 settlement to the PUC to resolve a similar complaint last July.
"There was no actual harm to Pennsylvanians, and the Commission subsequently approved the same operations," Uber said in a statement.
Two of the PUC's five commissioners voted against the fine. The penalty was "egregious" compared with more serious cases, some of which involved serious injuries or fatalities, Commissioner Pamela Witmer said in a statement.
Uber launched in Allegheny County, Pennsylvania, in February 2014, without getting commission authority to operate a taxi-like service. The company filed an application for two-year, experimental authority in April of that year, and the commission granted the application in July, about three weeks after its administrative law judges issued a cease-and-desist order.