Uber has violated zero-tolerance rules for drunken-driving on 151 occasions in the course of a year, out of a total of 154 complaints reviewed, according to findings revealed by the Consumer Protection Division of the California Utility Commission.

The commission's inquiry found the company had conducted follow-up investigations in only 21 cases, according to a Reuters report.

The commission recommended a fine of $1.13m (£903,096), which would be the first such citation against Uber or its rivals since the zero-tolerance rules were introduced in 2013.

The commission's findings come after a recent backlash against Uber and its senior management over its corporate culture and business tactics, besides sexual harassment complaints.

The investigation order, issued by the consumer protection and enforcement division of the commission on Tuesday (11 April), contains the drunken-driving findings.

An administrative law judge would examine those complaints and the proposed penalty and conduct further proceedings before recommending the case to the five-member commission itself.

A Uber spokeswoman told Reuters, "We've significantly improved our processes since then." She said the report is related to complaints registered two to three years ago.

"We have zero tolerance for any impaired driving," she said, citing Uber's "community guidelines". The guidelines state any driver found to be under the influence of drugs or alcohol while on the job will be "permanently deactivated: from the network.

"Uber may also deactivate the account of any driver who receives several unconfirmed complaints of drug or alcohol use," the guideline says.

The commission claims Uber received 2,047 zero-tolerance complaints across California against UberX and UberPool drivers during the year in question and dismissed drivers in 574 cases.