The Ministry of Business, Innovation and Employment (MBIE) says it has started an investigation into workplace conduct and culture at the Financial Markets Authority (FMA).

The FMA, the country's financial regulator, has been the focus of attention in recent weeks.

Chief executive Samantha Barrass went on leave last week after the board became aware of "cultural concerns".

It was announced in May that she would not seek reappointment when her term finished in January.

The announcement of her departure came shortly after the resignation of FMA chairperson Craig Stobo, after an independent review found his public commentary failed to meet the standards of political neutrality.

MBIE said the FMA board was supportive of the investigation, which would be led by Kristy McDonald KC.

"We are mindful this is an unsettling situation for FMA staff, and we will ensure the investigation is completed as soon as is reasonable," it said in a statement.

"MBIE will ensure the investigator provides an independent, confidential channel for people to engage with the investigation. Details on how this can be accessed will be shared shortly. We can make no further comment until the investigation is complete."