The Automobile Association is questioning a surge in the prices of petrol and diesel given the strength of the New Zealand dollar.
The association says the price of petrol has gone up 10 cents per litre over the past two weeks and diesel has risen 6c over the same period.
Spokesperson Mark Stockdale says while the harsh winter in the northern hemisphere has fuelled demand for heating oil, the high New Zealand dollar should have offset the worldwide increase in the cost of crude oil.
Don Braid, head of transport company Mainfreight, says fuel companies need to explain why their prices have risen and also believes the increases are not justified.
However Neil Green, from oil company BP, says the impact of the strength of the New Zealand currency has been countered by the surge in oil prices due to the falling value of the US dollar.
Smaller petrol station operator Gull says it will wait until Thursday before raising its prices.