Labour MP Carol Beaumont says it will be a terrible mistake if Parliament votes down her member's bill targeting loan sharks.
She says there are finance companies charging excessive interest rates and lending irresponsibly.
The Credit Reforms Responsible Lending Bill would set a maximum interest rate that could be charged, and require lenders to have a reasonable belief people are able to pay a loan back.
It is due to come before Parliament on Wednesday evening, but Ms Beaumont says the bill will not be supported by either the National or ACT Parties.
She says MPs should show rein in companies that target New Zealand's poorest people.
The Government says capping interest rates does not work because it then becomes a target rate for lenders.