A hearing into the use of the toxic gas methyl bromide in New Zealand has begun in Wellington.
The gas is a fumigant and is mainly used at New Zealand ports to ensure export logs are free from pests.
The Environmental Risk Management Authority hearing is aimed at reassessing the methyl bromide's use in New Zealand.
The Council of Trade Unions called for an immediate ban on its use.
It said there are scientific uncertainties surrounding the gases affect on humans such as links to motor neuron disease and other problems.
It believes the adverse affects of a ban would be outweighed by the benefits.
But MAF Biosecurity prefers a strategy of reducing and replacing methyl bromide.
Post border director Peter Thompson says many countries require imported logs to be fumigated with the gas.