Will the unions select Labour's next leader?

That puts the leadership in limbo for the next three weeks while up to 50,000 voting papers are sent out and candidates make their pitch at a series of meetings across New Zealand.

I suspect it will be far fewer than that. It is widely known Labour has less than 10,000 members despite my best efforts on their behalf.

[The pending leadership contest will be the first under Labour's new US primary-style system. If the leadership is contested, there will be a full membership ballot with the caucus getting 40%, party members 40% and affiliated unions 20%. CTU President Helen Kelly has said unions block vote for a single candiate - Editor.]

The six affiliated unions may have another 30,000 to 40,000 members between them but as I understand it most unions are not letting their rank and file members vote – just their union delegates, which are far fewer in number. By restricting it to delegates it will allow that union to promise its support more easily to the candidate who offers that union the most legislative favours.

Each delegate votes individually, and in secret, but make no mistake they will have been told the view of the union leadership about who to vote for and I predict that no union will be a close vote – the candidate the hierarchy supports will get at least 80% of the vote from that union. What is possible is different unions could vote different ways depending on what each has been offered, but Helen Kelly has already said they are talking to each other.

The new rules were an attempt by the party’s grassroots to rein in caucus after a widening rift over policy and direction. But they could drive an even deeper wedge if the party and caucus back opposing candidates and cancel each other out, because the caucus vote counts for only 40 per cent of the total.

That makes Labour’s union affiliates, whose votes count for 20 per cent, the potential king makers and could deliver the caucus a leader that a majority of MPs don’t support.

This will be the first time that corporate bodies will get to directly elect the leader of a political party. Imagine the fuss if for example you had business organisations getting a vote for a political party leader.

If Robertson and Cunliffe do stand, it is highly likely it will come down to who gets the unions on side – and that is easy. Unions will vote for what is in their best interest, so the candidate who promises them (publicly or privately) the most favourable law changes to increase their wealth and power, will get their support.