Te Pati Maori co-leader Rawiri Waititi is the highest-spending MP - in terms of Parliamentary Service funding

A new Taxpayers' Union briefing paper shows he spent almost 275-thousand dollars over the past 21 months.

It shows Labour's Damien O'Connor came in second - and the Greens' Huhana Lyndon third.

Union Policy Analyst Austin Ellingham-Banks says total MP spending reached 15-million dollars for the period, on travel, accommodation and transport.

But he says some spend far more than others, with no line-by-line tally to show why.