The government must reveal the daily oil price and conversion rates used to determine fuel pump prices to prove there are no hidden taxes, PKR vice-president Rafizi Ramli said.

Rafizi was responding to Domestic Trade, Co-operatives and Consumerism Minister Hamzah Zainuddin, who said yesterday he is unaware of hidden taxes and that retail prices for fuel are set according to the monthly average.

Opposition MPs claimed fuel pump prices are higher than they should be despite the government stating it is based on market prices, and that the differential is a hidden tax.

Rafizi said the monthly average is based on daily prices, which are converted from Singapore dollars.

"What is not known is the actual market price used for each day and the exchange rate to convert from US dollars to ringgit because it is published in Singapore.

"This is where they cheat. They cheat by 10 sen here and there but the effect is hidden taxes of RM150 million per month," he told Malaysiakini.

He said if Hamzah (photo) does not understand or cannot explain this "simple" matter, he should resign and give his job to someone who does.

Hamzah's predecessor Hasan Malek had in December 2014 promised to reveal the government's formula in determining retail fuel prices, but was dropped from cabinet the next year.

Asked on this yesterday, Hamzah said: “No, it is actually by the government, so it doesn't matter whether it is from my ministry or the Finance Ministry.”

Rafizi said it is "unacceptable" for Hamzah to say he is unaware as the issue of fuel prices has been in public discourse since the slide of oil prices in July 2014.

The Pandan MP said the issue has been raised multiple times in Parliament, while a demonstration was held over the matter on Dec 31, 2015.

Rafizi is also facing a defamation suit from Prime Minister Najib Abdul Razak and his wife Rosmah Mansor, for a speech he made on fuel prices at a political rally.