Labour state services spokeswoman Maryan Street asked Government whether it felt the report was robust.
She cited QC Bruce Corkill's legal opinion on the report, which said that it was unfair, misleading and contained flaws, basic errors of fact, and omissions.
Ms Street also asked why advice from senior civil servant Sir Maarten Wevers was disregarded by Ms Rebstock.
"The Government clearly has an agenda to appoint only those people who will tell it what it wants to hear," she said in a statement.
Mr Finlayson said he stood by the report and accused Labour of politicising the public service.
"On the core issue about politicisation of the civil service by the Labour Party, the report is very robust indeed," he said.
Mr Finlayson noted that it was an independent inquiry prompted by the State Services Commissioner, not by ministers.
Ms Rebstock is the Accident Compensation Corporation chairwoman and has previously headed the Commerce Commission and the Welfare Working Group.