A US plan to toughen sanctions against Iran over its nuclear programme could cut New Zealand exports there.
New Zealand's exports to Iran, mostly butter, are worth $224 million a year.
US senator Mark Kirk is preparing legislation which would blacklist Iran's entire energy sector and ban insurance or reinsurance services to Iran.
Blocks on bank payments and insurance deals for shipments could make even food sales hard to achieve.
Foreign Affairs Minister Murray McCully says New Zealand has fully implemented UN sanctions against Iran because of its nuclear programme and the sanctions will affect this country's trade.