Michael Stiassny, the long-serving chair of power lines company Vector, is stepping down after losing the support of the company's major shareholder.
Private consumer trust Entrust, which has a 75 percent stake in the energy distribution business, said it had advised Mr Stiassny it would not be supporting his re-election at the annual shareholders' meeting in September.
Mr Stiassny joined the Vector board in 2002 and has served as the chair for more than a decade.
In a brief statement, Entrust acknowledged the dedication and significant contribution Mr Stiassny made to Vector, but offered no explanation as to why it would no longer support his position as chair.
Mr Stiassny has also declined to provide further comment.