Wales' £6.9bn-a-year food and drink sector needs to be protected after Brexit, leading business and farming bodies have urged.
The CBI and the NFU Cymru have written a joint letter to 40 Welsh MPs, calling for support of the UK government's white paper, BBC Wales can reveal.
Welsh whisky distillery Penderyn said European trade was "enormously important" and it wants continuity.
Downing Street said its EU blueprint was deliverable.
But there has been criticism within Conservative ranks and inside the EU about the proposals, hammered out by the cabinet at Chequers in July.
The CBI-NFU letter also urges a bigger role for the Welsh Government in policy-making processes and for joint approaches with business and both governments to support businesses after Brexit.
It also wants Wales to keep its current share of farm funding when the UK leaves the EU.
Almost 75% of Welsh food and drinks exports go to the EU and the food supply chains are interlinked.
Many of the 240,000 workers in the industry are with small and medium-sized businesses and there is concern their voices are not being heard in the Brexit debate because they do not have the lobbying power of larger companies.
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Penderyn, the Welsh whisky firm based near Hirwaun, Rhondda Cynon Taf, exports a quarter of its bottles.
Stephen Davies, chief executive, said his main concern was the continuing uncertainty and any problems in importing and exporting would be an issue - with no deal being a worst case scenario.
"Europe is very important to us as a business - we bring some raw materials in, glass from France - but also exports. We export a lot into France and Germany in particular but to most parts of Europe," he said.
He agreed other overseas markets offered potential.
"There are opportunities there but I think for a business like ours, to be able have continuity of being able to trade with Europe is enormously important," said Mr Davies.
"Exports are a growing part of our business - around a quarter of our business - but we plan to increase that significantly over the next few years and some of the biggest markets for single malt whisky are in Europe and so we can't afford to be complacent or ignore those markets."
John Davies, president of NFU Cymru, who farms near Brecon, wants clarity and a "pragmatic and sensible approach".
"We were pleased to see agri-food was in that deal and that it included free and frictionless trade with the biggest and best marketplace for our produce - we're really keen to see that delivered."
The issues are not just around avoiding tariffs but also continuing cooperation on issues like food safety standards to ensure products can easily be traded across borders.
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The letter supports a common rulebook with the EU, to underpin highly complex food supply chains. It says an "equivalence with the EU will be highly reassuring".
CBI Wales chairman Mike Plaut, said people did not realise how important the food and drink sector was.
"In Wales, we've got some really good agri-businesses and we need to start championing them and making sure that Brexit doesn't damage them."
Former Brexit Minister David Jones said on Monday he believed the deal, negotiated at Chequers, was "at an end".
The Clwyd West MP added: "I think in reality Number 10 have nothing to do but look at Chequers again and come up with an alternative solution."