NEW FOCUS: Police are checking with passengers about how their fares are being worked out.

Auckland police are questioning Uber passengers in their crack-down on the driver-on-demand system.

Holly, a 26-year-old woman who did not want her surname used, said she was in an Uber car at Auckland's ferry terminal on Saturday.

A police officer in an unmarked police car stopped the car and questioned her telling the driver to stay away while she was grilled, she said. Holly said the officer pulled her aside and asked how she ordered the vehicle and whether they had agreed a set price before the journey.

When she said "it (the Uber app) tells me at the end", the officer turned his attention to the driver.

Holly said the officer told her that Uber was illegal in New Zealand.

It's not, but the manner of billing passengers is what has caused contention. Uber operates as a private hire service which means the fare has to be set at the time of booking, rather than using a meter.

Police have confirmed they have stopped several Uber drivers and charged them or issued them infringement notices for using their smartphoneapp as a meter - a breach that would make them subject to taxi regulations.

Two drivers are reportedly before the courts on charges. Several people have reported being in Uber cars stopped by police, including Auckland DJ Tim Phin who posted his experience on Facebook.

Uber spokeswoman Katie Curran said a number of precedents around the world determined that smartphones were not taxi meters.

"Uber believes policy makers in New Zealand could reasonably come to the same conclusion, rather than having this debate played out over a potentially lengthy period which is not in the public interest." She said one particular police officer had targeted several drivers.

"This officer's actions have also put riders at risk when he ordered them to vacate the vehicles, leaving them stranded at night with no other travel options to get home."

Inspector Jim Wilson, Auckland City Police Acting District Commander, said police took public safety seriously. Passengers in affected vehicles were either dropped in central Auckland or driven home by police.