Contact Energy has lost thousands of customers in the past year.

The company's latest operating statistics show electricity, gas and LPG customer numbers fell to 597,500 at the end of May, down from 601,000 a year before.

The slide in numbers started after controversy over directors' fees in 2008 - when it lost 40,000 customers in six months - and has been exacerbated since by unprecedented competition for retail consumers.

Two years ago Contact had 520,000 electricity customers alone, this figure is now down to 476,500.

Contact has, however, staunched the flow in the past two months with the number for May identical to that at the end of April. A spokeswoman said the arrest in the decline was because of its current offers.

However, the company could face unhappiness among its 22,500 customers in Dunedin where it will put up prices by 10 per cent from July 1.

After the announcement Energy Minister Gerry Brownlee issued a statement urging consumers to shop around for the best deals.

He advised them to use the Consumers NZ's PowerSwitch website and his office said those without internet access could phone the institute for an estimate of what of what they could save.

The Contact spokeswoman said prices were increasing partly as a result of the Government's emissions trading scheme which comes into force for power companies on July 1.