Proponents of genetically modified or genetically engineered crops say they are quicker and cheaper to grow and could help solve world hunger. Opponents charge that the health effects of such foods are not known and consumers have the right to know whether what they buy is modified.

Two weeks ago, Canada's Parliament defeated a bill to support mandatory labeling, prompting Greenpeace campaigner Pat Venditti to say that grocers, the biotech industry and the government "seem to be in bed together.

"They are taking a stick-your-head-in-the-sand approach, waiting till this all goes away. They do not have any justification for not labeling," Venditti told Reuters.

Catherine Lappe, a spokeswoman for Rock, said the health minister supports labeling despite the defeat of the mandatory labeling bill in Parliament.

"Minister (Rock) has made it very clear that he does support mandatory labeling," Lappe said. "The bill that was defeated is not the only way to get there. A number of ministers have asked (Parliament's) health committee to review this. The forum now for mandatory labeling to be considered is through the health committee."

Loblaw spokesman Geoffrey Wilson told Reuters the Canadian government has no standard yet for defining which foods are genetically modified and which are not.

He said that is why, earlier this year, Loblaw and several other Canadian grocers told suppliers to stop making claims on their labels that their products were free from modification.

"The whole agricultural food chain cannot readily segregate foods to an appropriate extent that would allow labeling at this point in time," Wilson told Reuters.

"Our position is that our government determines what food goes on our shelves, and we certainly abide by those rules."

Greenpeace said it targeted Loblaw because it is the country's largest grocer and advertises itself as a company that listens to its customers' needs.

"If that were the case, they would start at least labeling food for their customers," Venditti said, adding that a recent Greenpeace survey found that 95 percent of Canadians want mandatory labeling.

Wilson said there are extra costs for grocers to label food but added that it is premature to estimate how much.

But Venditti said that some European retailers, who are "light years ahead of Canada" in terms of labeling, have found it relatively inexpensive.

A letter written in August by big British supermarket chain J. Sainsbury Plc to Greenpeace says the British grocery giant removed genetically modified ingredients from its products and introduced labeling without any cost to the consumer.

Venditti said Sainsbury's, Tesco Plc , another British food-store chain, and French retailer Carrefour already label their foods.

"It is insane how far behind we are," he said.

Wilson said the reason European retailers are labeling and Canadians not is because Canada has stronger food safety laws and a healthier food system.

"If you did any research, you would find that in Europe anything goes. They are making genetically-modified-free claims without any backup," he said.

"We have a much healthier food system than Europe. That's why a lot of this came to pass there, and the advocacy groups took advantage of that system that was rife with issues."