The Automobile Association says a seven cent jump in the cost of petrol and diesel in the past week is unjustified.
Its policy analyst and petrol watch spokesperson, Mark Stockdale said there were three increases during the week, taking the price of 91 octane to $2.10 a litre and diesel to $1.36.
He said petrol companies were trying to justify the increases as a way to cover commodity prices.
"The bottom line for us is that the commodity price for petrol and diesel did not rise the equivalent of seven cents a litre in the past week."
Mr Stockdale said commodity prices had been rising and there was volatility in the exchange rate but that had not justified the seven cents increase.
He said if anything petrol companies could have afforded to drop their prices.
However, BP New Zealand has hit back at the Automobile Association's criticism of it increasing petrol prices.
BP communications manager Jonty Mills said there were a number of factors that drove petrol prices.
He said last week's price increase was prompted by the exchange rate and the cost of the product on the international market.