In the absence of an international standard, several countries are starting to introduce their own labelling requirements for GM food. The United States and Canada, two main producers of GM crops, are taking a selective - and least-stringent - approach. The US has a voluntary system whereby GM food is labelled only if it is 'not substantially equivalent to its conventional counterpart' or if it contains an allergen consumers would not normally expect in the food to be labelled. Canada has adopted a similar approach, except that labelling is mandatory where GM food is considered to be a health or safety concern, for example if the food contains allergens. The European Union, Australia and New Zealand have opted for a threshold-based mandatory system, where a food product containing more than one per cent GM content in any one of its ingredients has to be labelled. The EU requirements took effect in April last year, while Australia and New Zealand will introduce mandatory labelling in December. In Japan and South Korea, only food containing the most common GM crops, such as corn and soybean, have to be labelled. Japan has adopted a threshold of five per cent, while Korea has set a limit of three per cent. Japan's labelling requirements will come into effect in April and South Korea's in July.