Errington said the authority followed the same procedure every year. "The reasons are quite simple. We are a follower of trends rather than a setter of trends so we wait until we've got all the information we need and make sure it's all up to date and then we set the remuneration. Therefore we backdate it to July 1."
Taxpayers Union spokesman Jordan Williams said this showed politicians' pay was disconnected from economic reality.
"A post-election bonus is just outrageous," he said.
"By doing it that way, they're effectively ruling out pay decreases. If they take [pay] down, what are they going to do? Send each MP a bill? It shows it's a farce."
The union advocates tying politicians' pay to the country's economic fortune, measured by the gross domestic product.
The Prime Minister's salary has increased by $53,5000 since 2007 to $428,500.
The Leader of the Opposition, the Speaker and Cabinet ministers are now making $268,500, $35,000 more than they were paid in 2007, and backbench MPs get $147,800, a $21,600 increase over the same period.
Including a zero rise in 2009, the Prime Minister has had an average annual pay increase of $8900 since 2007, the Leader of the Opposition, the Speaker and Cabinet ministers a $5900 increase, leaders of minor parties a $3800 increase and backbenchers a $3600 increase.
Green Party co-leader Russel Norman, whose party wants to lock politicians' pay to the national median income, said the back-dating system was "unfortunate".
"Hopefully , we'll be in a position to introduce a new policy by the time it comes around to recalculating MPs' salaries."
