An employment law expert says a firefighter who used an obscene gesture about the Prime Minister brought Fire and Emergency into disrepute. 

A clip posted on social media shows Chris Luxon speaking with a person before heading towards a Defence Force helicopter.

The volunteer firefighter then turns to the camera and makes an obscene gesture.

Fire and Emergency is now investigating. 

Employment law expert Max Whitehead says volunteers don't have the same rights as a career firefighter, and explained she wouldn't be able to sue the organisation if she were fired. 

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