A potential free trade deal between the UK and New Zealand after Brexit could price Welsh lamb off the shelves, a farming union has warned.
This week Theresa May announced the UK should leave the single market when Article 50 is triggered.
But the Farmers' Union of Wales fears a "hard Brexit", plus a potential deal with New Zealand, could be damaging for Welsh farmers.
Conservative AM Paul Davies said the industry had to remain "positive".
About 90% of Welsh food and drink is currently exported to the EU.
FUW president Glyn Roberts said the industry was facing a "perfect storm" if a trade deal was struck with New Zealand and a hard Brexit was pursued.
Mr Roberts said Welsh lamb would have to compete with a country that is in direct competition with it and able to sell at a much cheaper price.
He told BBC Wales: "In no way can we compete on price with New Zealand, but we can compete on value, and what we have as a premium product in Welsh lamb.
"It depends on what the consumers want: does the consumer want cheap food or does the consumer feel that by buying Welsh products and Welsh lamb, that they are getting a premium product," he added.
Last week, Theresa May said the UK government would begin talks with New Zealand with the ultimate aim of striking a trade deal.
But Mr Roberts said UK farmers could sell much more to the 500m people living in the European Union - some 20m across the channel - than about 4.5m people living in New Zealand.
"It is a perfect storm because what we in Wales want to export is exactly the same thing as New Zealand want to export to Wales," he said.
"Getting a deal with one country is one thing, getting the product there and marketing the product is another thing."
His daughter, Becca, 23, said she felt uncertain about her future on the family sheep and beef farm near Betws-y-Coed, Conwy county, following the Brexit vote.
"I just came back from university, it is very worrying," she said.
"I have always wanted to farm sheep and beef, I will have to think about something else."
Pembrokeshire Conservative AM Paul Davies said while farmers faced huge challenges Brexit presented opportunities as well.
"What's important now is that we get the best possible access to the single market, and I think Theresa May made that absolutely clear in her speech," he said.
"We have to remain positive because of course the sustainability and future of agriculture depends upon it.
"That's why, in my view, the UK government should prioritise agriculture as a sector when they enter into negotiations with the EU."