Andrew Little says in the wake of the Roger Sutton sexual harassment claims, state services commissioner Iain Rennie is "unfit" to do the job.
Mr Sutton, the Canterbury Earthquake Recovery Authority (Cera) chief executive, resigned on Monday at a joint press conference with Mr Rennie.
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Mr Little, the new Labour party leader, told TV One's Q & A programme the announcement of Mr Sutton's resignation was not handled appropriately and Mr Rennie must be investigated.
The Labour leader said it was odd Mr Sutton was able to give his side of events while confidentiality orders gagged the victim from speaking up.