The Commerce Commission has asked the Interislander ferry service to stop advertising its fares with a separate three dollar per person "fuel surcharge", saying the company should be incorporating the cost of fuel into its overall prices.

The Interislander recently introduced a "fuel surcharge" which is separately disclosed on its website and on its tickets. Complaints from the public sparked the Commerce Commission's request to change the way it advertises its fares, and the Commission has opened an investigation into the company's advertising.

In November the Auckland District Court, considering a Commerce Commission case brought against Air New Zealand, ruled that the cost of fuel is an operating cost and should be included in the price of travel, not separated out as a surcharge.

In his judgement, Judge Thorburn said that the Air New Zealand advertisement in which fuel costs were charged separately "smarts most unpalatably of "sharp" and unacceptable practice."