Some Northlanders are paying nearly 20 per cent more for power than they were three years ago.
Figures supplied by Consumer New Zealand show households in Whangarei and Northland rural areas are paying about $2450 a year, compared with $2050 in April 2009.
Empower, wholly owned by Contact, is again the most expensive among the five suppliers in both areas, with households paying an average $2450 a year compared to $2050 in April 2009.
That is a 19.5 per cent increase.
Meridian is the next most expensive at $2300 - up from $1990 three years ago, followed by Mercury and Genesis at $2220, compared with about $1950 in April 2009.
The prices are for the most common plan for a household of three to four people using electric water heating, electric cooking, and a mix of electric and other space heating such as wood burners and gas heaters.
Last month, Mercury and Contact announced a price increase in Northland of 5.8 per cent and 14 per cent respectively.
The latest hike by Mercury followed similar rises of 3.3 per cent in 2010 and 3.5 per cent in 2011.
Contact's 14 per cent increase follows a 7 per cent hike it announced last year.
Consumer NZ has advised users to constantly check for cheaper suppliers and to switch if it means savings.
Last year, Mercury introduced a three-year fixed plan for selected Auckland customers and later introduced it in Northland.
Consumer NZ has warned consumers against signing up for Mercury's fixed price plan, which locks them in for three years.
Although those that sign up are not affected by price movements for the duration of their contract, they have to pay a $150 fee should they wish to change supplier or move to an area not covered by Mercury.
"Firstly, you'll have to pay more initially. Consumer NZ estimates that the fixed rate Mercury Energy offers is 9 per cent more than existing tariffs," a spokesperson said.
It means any customer signing up to the deal is agreeing to a 9 per cent increase in their electricity prices over the next three years, which must be paid from when they sign up.
"Mercury Energy also increased its prices by 4 per cent in April this year, after the deal was initially launched, so anyone signing up to the deal now will be agreeing to pay 9 per cent on top of that 4 per cent increase."
Before households signed up to the Mercury plan, Consumer NZ suggested they did some number crunching via Powerswitch to see how competitive other retailers may be.
A Mercury spokeswoman said the three-year fixed plan offered a good deal and had been taken up by more than 80,000 customers nationwide.
However she said it was not for everyone and Mercury would never wish for its customers to feel pressured to accept a plan they felt didn't suit them.
Customers who signed up had 30 days to exit from their contracts if they changed their minds, she said.