Parliament is debating legislation under urgency to remove the right of beneficiaries to claim back payments for an error in the law that has been in place for 20 years.
RNZ reported in September that, since 1998, the government had been starting payments the day after a beneficiary's stand-down period ended.
Since then, advocates have been helping people claim the extra day's pay, sending out hundreds of review forms, which are forwarded to Work and Income.
MPs are now debating legislation introduced to retrospectively change the payment date to the day after stand-down.
Greens co-leader Metiria Turei said the law change was outrageous.
"The government will put in legislation to make it harder for people to have access to this one day's pay, and then chase down teachers with debt collectors. The bill is totally unjust."