Trump-style economic protectionism could have devastating effects around the world, Federated Farmers say.
It said the US president's willingness to shun international trade conventions would have serious and deeply felt implications for New Zealand exports.
Federated Farmers president William Rolleston said because New Zealand was small, it could not afford for those conventions to be sidelined or for a trade war to break out.
"This is extraordinary. If allowed to continue in this vein, it will undermine all the work we've done as a nation.
"We have long advocated for countries to live up to their commitments and obligations. This thinking will take global trade backwards and will ultimately be as damaging for the US as anywhere else," Dr Rolleston said.
New Zealand's standard of living was intimately linked to being able to sell goods and services overseas, he said.
"The government [does] need to make sure that we've got good resources up in our foreign trade sectors, that we are proactive [on maintaining conventions]," he said.
"We're not just talking about the United States, we've got Brexit going on as well, and we're trying to develop free trade agreements in Europe and a number of other countries, Mexico included.
"So we need to keep on that steady path and not get distracted and sucked into something that would be detrimental to trade across the world, and, in the end, detrimental to us," he said.
"We have worked so hard, for so long, to get our products to more than 120 countries around the world.
"If President Trump decides to use the might of the USA to bully their way out of trade agreements, which were negotiated in good faith and to be mutually beneficial to all parties, then New Zealand and many other countries could be severely compromised," he said.