After the government blocked an inquiry into banks, Labour, the Greens and the Progressives have decided to hold their own one.
Labour finance spokesman David Cunliffe said the parties were concerned by high interest rates.
"Banks believe interest costs are justified. The facts should be put on the table fairly and openly so that people can see whether they are receiving a fair deal," he said.
Reserve Bank governor Alan Bollard recently said interest rates were too high and it would have been useful to hold an inquiry.
Government MPs on the parliament's finance and expenditure select committee on July 1 blocked one from going ahead.
"The inquiry being announced today would have a similar primary focus as that originally agreed by the select committee," Cunliffe said.
"It will be an inquiry into the relationship between the official cash rate and short term interest rates, in the context of matters raised by the finance and expenditure committee in its report on the Reserve Bank of New Zealand's financial stability report."
All parties would be invited to participate as well as organisations and businesses, including banks.
Bollard would be asked to seek approval from Finance Minister Bill English to give evidence.
The inquiry was seeking logistical support that committees normally received.
"This is a serious inquiry by parliamentarians on behalf of New Zealanders. We believe it is appropriate support, including a venue, is made available, so that the public and media can attend."