The agricultural chemical industry has accused the Environmental Risk Management Authority of acting too fast in banning the insecticide endosulfan.
The authority prohibited the importation, manufacture and use of the chemical last month as part of a review of pesticide use.
Endosulfan has been used to kill insects on vegetables, some fruit crops and ornamentals and to control earthworms in turf.
The body representing agricultural chemical and animal remedy companies, AGCARM, has warned that the insecticide's rapid removal could result in illegal dumping.
Chief executive Graeme Peters acknowledges the authority has been proactive in telling people where they can dispose of endosulfan stocks, but says many will not do that and will, instead, dump the chemical.
Mr Peters says that will be bad for the environment and have the opposite effect to that intended by the authority.
He says suppliers have incurred the cost of writing off their stocks of endosulfan.
The chemical industry organisation has no problem with the de-registering of chemicals but Mr Peters says it would have been wiser to phase out the use of endosulfan over several years.