A plant nursery fears losing £500,000 a year due to a post-Brexit soil ban preventing sales to Northern Ireland.
North Yorkshire firm Johnsons of Whixley has called for urgent action over rules it "didn't see coming".
Soil from non-EU states cannot be taken into NI, which remains within the bloc's plant health system.
The Department for Environment, Food and Rural Affairs (Defra) said it was providing assistance to the horticulture industry.
Irish Sea border arrangements mean Northern Ireland must apply EU rules on products entering from Great Britain.
Plants now need a health certificate to enter but soil, which can carry pests and diseases, is among products that are completely banned.
Horticultural Trades Association (HTA) chair James Barnes previously told the BBC some of its members in Great Britain were reconsidering trade with NI as a result of added regulations.
Jonathan Whittemore, head of production and procurement at Johnsons, said the firm "didn't see this coming at all".
"It basically means we can't sell plants now into Northern Ireland.
"Talking to our plant health officer, it became apparent that actually any plants that we'd grown on the nursery here in Yorkshire or brought in from other parts of Europe or other parts of the UK and stood down on the ground here would not be able to go into Northern Ireland.
"They need to be completely free of any traces of soil."
"We need the UK government to be working with the EU administrations and coming up with a solution," he said.
"Nothing has changed for us," he said, adding that the firm had been trading with NI and EU countries for years, "never with any issue".
"We're now caught up in legislation that we didn't see coming, that shuts off trade into customers that we've happily dealt with for a long time."