The investigation into suspended Green MP Darleen Tana has cost $43,000 so far.
The list MP was stood down on 14 March, after allegations of migrant exploitation relating to her husband's e-bike company surfaced.
The money has come out of the Green Party leaders' office budget, which is funded through the Parliamentary Service, paid for by the taxpayer.
"Natural justice is important to the Green Party and that's why an independent investigation into the very serious allegations surrounding Darleen Tana is taking place, which has so far cost $43,000," a Green Party spokesperson said.
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She has been off work and away from Parliament for half its sitting days this year, while continuing to collect her full pay.
Greens co-leader Chloe Swarbrick told Morning Report on Monday that the investigation report was out of her hands but was hoping it would be wrapped up soon.
The investigation, led by barrister Rachel Burt, has now lasted nine weeks but is yet to report back, with the party co-leaders not setting a deadline.
"I think the natural justice process requires that people are not suspended without pay on the basis of those allegations alone. Again, that innocent until proven guilty principle is critical in a country like ours," Swarbrick said.