Food safety watchdogs are to begin testing milk from farms fertilised with oil and gas drilling waste.
But the Green Party argues the practice is pollution - and the new testing regime is "too little too late", after almost two years of negotiations.
The controversial method of "land farming" involves spreading mud and other waste into poor quality soil, which is then returned to pasture.
Green MP Gareth Hughes said a 2005 report showed cows were grazing on a dump farm with elevated levels of hydrocarbons, but almost a decade had passed without a testing regime for petroleum toxins.
He believes oil and gas extraction should not take place close to primary productive land: "Cows are allowed to graze on land with high levels of hydrocarbons without any punishment and their food products are allowed to go to market without government testing."
There were 12 land farms in Taranaki, and more than 30 sites where petroleum industry waste was buried, he said.
However, Federated Farmers president Bruce Wills said his organisation would "be guided by the science not the emotion".
A report by soil scientist Doug Edmeades, commissioned by Taranaki Regional Council, concluded levels of nutrients, heavy metals and soluble salts was similar to regular soil. "In his words, it is just dirt," Mr Wills said.
But he added: "I would support MPI doing random sampling. No-one wants to put our world class reputation at risk by having any substance in the soil that shouldn't be there."
Ministry for Primary Industries director market assurance Tim Knox confirmed discussion on land farming began in mid-2012. Farmers must now notify their dairy company if industrial wastes were applied to their land.
The ministry was working to identify land farms to include in a contaminant monitoring programme, he said. Targeted random testing from land farms in Taranaki would begin in the "next couple of months".
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