The Greens are calling for New Zealand to stop being the only country preventing an international agreement on genetically engineered organisms.
Green Party MP Nandor Tanczos said it was shameful New Zealand had not signed the Cartagena Protocol, which came into force in 2003.
The protocol required exporters to provide more information about GE products like maize and soybeans to recipient countries to help them decide whether to accept them.
Under its provisions, a nation may reject GE crops or seed -- even without scientific proof -- if it fears they pose a danger to traditional crops, undermine local cultures or cut the value of biodiversity to indigenous communities.
Talks are underway this week in Curitiba, Brazil.
"We have been the object of international condemnation for some time for being on of the countries to block agreement. Now to our shame we stand alone in wanting to deny developing countries the protection of a robust international standard," Mr Tanczos said.
"We have strong rules at our own borders but are seeking to deny that to the countries that cannot afford the kinds of testing regimes we have in place.
It is a shameful stance. "
He said the Government was behaving like an international vandal.
Mr Tanczos earlier said New Zealand was acting on behalf of the United States which is not a party to the talks.
Yesterday Acting Prime Minister Michael Cullen denied that.
"This Government does not act as a stalking horse for the United States in any matter at all," said Dr Cullen, who is also acting Foreign Minister.
About 132 countries have signed the treaty, but not the United States, and it has no vote on issues such as how shipments should be labelled if they have unintended genetically engineered (GE) content.
Mr Tanczos questioned the Government's motives after NZ and Brazil were the only countries which stopped 117 other signatories reaching a consensus on labelling at the previous round of talks in Montreal last year. Brazil has now changed its position.
Dr Cullen said New Zealand supported meaningful and informative labelling of GE organisms. "We think it is important to have simple, practical, workable, and implementable documentation requirements."
Dr Cullen said New Zealand would not support accidental inclusion of GE content as requiring that content to be listed on the shipment documentation, because such a provision could catch conventional agricultural shipments, even of crops produced to organic standards.
Ordinary crops would have to be labelled "may contain living, modified organisms" because of the remote possibility they might have come into contact with living, modified organisms, he said.
The Cartagena Protocol, which came into force in 2003, requires exporters to provide more information about GE products like maize and soybeans to recipient countries to help them decide whether to accept them.