New Zealand's largest gas distribution company, Vector, is being accused of overcharging customers.
Industry regulator the Commerce Commission is proposing pricing changes that would cut the bills of Vector's 144,000 residential gas customers by up to $5 a month.
Vector would have to cut prices by an average of 16% for local networks serving households and 25% for large pipes serving big companies.
Its biggest rival, Powerco, could raise its distribution charges by 5%, which means its 101,000 customers would pay 60 cents more a month.
Vector chief executive Simon McKenzie says gas companies are already fighting the methodologies used to set the prices in court.
Mr McKenzie believes the commission's methodology is flawed and its ruling contradicts government policy favouring robust infrastructure.
"One week we can have the Minister of Energy talking about the critical nature of infrastructure, and then we get the commissioner basically saying they're going to significantly cut our operating costs, they're going to significantly cut our capital expenditure."
Mr McKenzie says the proposed pricing changes would have a big impact on Vector's capital expenditure.
The Commerce Commission says Vector could apply for a customised pricing path to enable it to carry out costly projects, but it would be subject to scrutiny.
Also under the draft proposal, GasNet's 10,000 customers in Whanganui would be paying $1.10 less a month and Maui Development would raise its transmission charges by 2%.
The commission says the gas companies should limit price increases to no more than the rate of inflation until 2017.
Vector and the commission agree that if the company wins in court, the entire price control methodology for pipes and wires will have to be redesigned.