The Forest Owners Association has told the Environmental Risk Management Authority that the use of the chemical methyl bromide to treat logs is essential until an alternative fumigant is found.

ERMA began a series of hearings in Wellington on Monday to decide whether to allow use of the chemical for another 10 years.

It's a colourless, odourless gas mainly used at ports to spray export logs to keep them from pests.

But many people object to its use as it’s toxic to the human nervous system and depletes the ozone layer.

The Forest Owners Association’s senior policy analyst Glen Mackie defends its use.

But the Council of Trade Unions wants an immediate ban on its use.  Victor Billot, spokesperson for the Maritime Union, says the chemical is too risky for workers.