The New Zealand Institute of Economic Research predicts the loss of 20,000 construction jobs by 2012.
The institute says the job losses will come in non-residential construction, which it says is on the verge of collapse.
It says consents fell by a third a year ago to record lows and show no signs of a quick recovery.
The institute says infrastructure works from the Government could pick up some of the slack.
But the Building Trades Union says building new roads and bridges will suit the skills of only some of its members.
The union says many tradespeople will not wait till 2012 for a recovery and many are already moving to Australia.
