The Electricity Authority is investigating concerns about energy pricing, contract availability and business conduct in the electricity and gas markets.

The authority said the investigation followed concerns raised by the Northern Infrastructure Forum and other organisations.

"We take all concerns raised seriously, and any concerns related to consumer trust or market fairness demand attention," authority chair Anna Kominik said.

"We have started a review under section 16 of the Act focused on business consumers' access to electricity contracts, including commercial and industrial consumers."

Section 16 enabled the authority to use formal information gathering powers to look more closely into pricing and other terms offered to business consumers.

The authority said it was working closely with the Commerce Commission, which recently launched a new whistleblowing tool to make reporting easier.

The authority said the scope and timeframe of the review would be refined as the investigation developed.

Meanwhile, big electricity retailers will have to offer cheaper prices for off-peak power use prices, and fair prices to people who sell surplus power to the grid from roof top solar panels at peak times.

The Electricity Authority announced last month it was changing sector rules to require retailers with more than five-percent market share to offer time of use prices from the middle of next year, after a report by a joint task force of the authority and the Commerce Commission.

The changes were aimed to give consumers more choice in how and when they use power, and put downward pressure on prices.

Also last month, a letter was sent to Prime Minister Christopher Luxon calling for an urgent reform of the sector as soaring power prices undermine confidence and productivity.

It took aim at the four big power generation companies Genesis, Contact, Mercury and Meridian, also referred to as gentailers, because they compete at the retail level.

It was signed by groups representing big and small energy users, small retail energy suppliers, and a cross-section of industry organisations representing a broad range of sectors.