The Green Party says Wellington's port needs to come clean about how much of the toxic gas methyl bromide is being released into the local atmosphere.
The poisonous chemical is used to fumigate containers leaving for and arriving from overseas.
Green Party biosecurity spokesperson Steffan Browning said he applauds CentrePort for honouring its pledge to begin recapturing all methyl bromide released from container fumigations by the end of last year.
But he said it needs to make it clear it isn't recapturing the methyl bromide released when log shipments are fumigated.
Mr Browning said when two holds of logs on a vessel were recently fumigated more than a tonne of methyl bromide was not recaptured.
He said the gas depletes the ozone layer and puts the health of workers and local communities at risk.