Opposition MPs are questioning why the Remuneration Authority releases politicians' new pay rates just before Christmas when this means the increase has to be backdated.
Politicians have been given a wage rise of 1.9% backdated to the beginning of July.
The prime minister will now get $419,300 a year, up from just over $411,000.
The pay for backbench MPs goes up from $141,800 to $144,600.
The Green Party says there is no good reason for the timing, which causes controversy over back pay.
Mana Movement leader Hone Harawira says the announcement creates resentment among the public who find late December a stressful and expensive time of year.
The Public Service Association describes the move as straight out hypocrisy, saying back pay is not allowed in public service negotiations.
The Remuneration Authority was unavailable for comment.