A Department of Agriculture investigation has been launched into a report that contaminated maize was imported here from the United States in early April.
Greenpeace International and GM-Free Ireland Network said a shipment of animal feed intercepted in Dublin port and later in Rotterdam had entered the EU illegally.
Greenpeace said the cargo was contaminated by unauthorised and toxic varieties of genetically modified (GM) maize called Herculex, which is approved in the US but illegal in the EU.
On Monday the EU said that if this proved to be the case, the cargo would have to be sent back to the US by the Dutch authorities.
An EU spokesman said this material was not harmful to public health but because it had not been sanctioned by the EU authorities, it was unlawful at the moment. "Should our tests confirm what Greenpeace is saying, then the cargo will have to be returned," he said.
A spokesman for the Department of Agriculture said it would be asking the Dutch authorities for information on the cargo.
A spokeswoman said that when part of the cargo was off-loaded here on April 2nd, it was described as "non-GM" by the US authorities and had not been tested.
"We are now in the process of attempting to find out as much as we can about the location and what the imports contained and we expect more on that later on Wednesday, as it is a public holiday in the Netherlands today," she said.
GM-Free Ireland Network said the cargo unloaded in Dublin was GM soya hulls and distillers grain from GM maize, but it did not have the result of tests from the Irish part of the cargo as yet.