Opposition leader Andrew Little says Labour will consider forcing banks to pass on cuts in the Official Cash Rate (OCR) to customers if they did not respond to a "stiff-arming".
Mr Little's comments come after several of the main banks only cut their interest rates on loans by a portion of last week's 0.25 point cut, down to 2.25 per cent.
Mr Little said if Labour was in government it would start with "pretty serious talking" with the banks.
"And if they are not responsive to that you've got to look at your options. I mean you're in government, you have the power to legislate. I wouldn't rule it out and if we did it, it would be with great reluctance and a heavy heart."
He said the banking sector had been very profitably through good and bad. "I think, frankly, they can do better for New Zealand."