Today's revelations about Syngenta, the supplier at the centre of the Corngate affair, illustrate the pitfalls of a GE-monitoring system that takes seed manufacturers at their word, the Greens say.

"If seed companies are so careless or dishonest that we can't trust that the seed they're supplying is what they say it is, then our entire GE-monitoring system is called into question," Green Co-Leader Jeanette Fitzsimons said.

Syngenta has admitted to US authorities that for three years it sold genetically-engineered corn seed that hadn't been approved for sale, and Ms Fitzsimons said it was time for governments around the world to stand up to the seed manufacturer and demanded it mend its socially irresponsible ways.

"Syngenta has developed a reputation for thinking it is above the law, and for refusing to provide regulatory bodies with information that is needed to assess whether its activities are in the public interest. It's time our government told Syngenta that if it doesn't make itself more transparent, trustworthy and accountable, it is not welcome in New Zealand.

"The select committee inquiry into Corngate failed to get to the bottom of that matter because Syngenta refused to allow our Parliament to see lab records or talk to the company who did the testing that showed Bt contamination. Now, they are similarly refusing information to the US authorities. They won't say which countries they have exported this contaminated corn to. Surely the unsuspecting farmers and consumers who have been misled about what they are planting or eating have a right to know?"

Ms Fitzsimons said the Syngenta revelations were one more good reason not to allow the growing of GE crops here.

"It's bad enough if you get the GE crop you think you're ordering, but it now seems you may get something illegal instead. This case illustrates how illegal seed, which hasn't gone through proper safety checks, can get into the food chain. Syngenta did not discover the error itself - a seed breeder did. It makes you wonder how many other mistakes they have made which are still undetected.

"The US Government claim that this corn is 'safe' is ridiculous. There has been no time for any safety testing since the error was discovered. It is clearly different from the approved corn and no-one has investigated whether the genetic differences might cause harm to health.

"New Zealand's food safety regulatory body - FSANZ - uses the same criteria as the US Food and Drug Administration to decide whether a food is "safe". We must stop relying on slack procedures and false assurances of safety from the US."