Downing Street's warning that Brexit talks with the EU are "over" is "hugely concerning" for farmers, the president of a farming union has said.
No 10 said there was "no point" in discussions continuing next week unless the EU was prepared to discuss the detailed legal text of a partnership.
John Davies, from NFU Cymru, said farmers face an "incredibly difficult marketplace" if there is no deal.
The Welsh Secretary said businesses needed to prepare for new trade rules.
Prime Minister Boris Johnson had set this week as a deadline for the end of trade talks, with the Brexit transition period coming to an end on 31 December.
However, there are still major differences between the two parties over fishing rights and state help for businesses.
UK chief negotiator Lord Frost said he had told EU chief negotiator Michel Barnier there was no "basis" for planned talks on Monday.
Number 10 said the two sides had agreed to talk again, by phone, next week.
Importance of market 'cannot be overstated'
Mr Davies, of the National Farmers' Union (NFU) Cymru, urged the UK and EU to continue talks.
He said: "News that the UK should ready itself for a 'no deal' is hugely concerning for Welsh farmers and the thousands of people and businesses whose livelihoods depend on the sector.
"The importance of the EU export market to the Welsh farming industry cannot be overstated.
"Under a no deal scenario agri-food products would attract eye-wateringly high tariffs, effectively pricing Welsh farmers out of their nearest and most lucrative export market.
"With the transition period due to end in just 10 weeks, if we are indeed heading for a no deal outcome, then this leaves businesses with little time to prepare, particularly the farming industry given the long-term production cycles the industry operates to.
"It would mean farmers very shortly finding themselves operating in an incredibly difficult marketplace and one which would be completely at odds with what was promised by those advocating Brexit."
'Vital' businesses prepare
Meanwhile, earlier on Friday, Welsh Secretary Simon Hart told business groups that it was "vital" businesses prepare for a new relationship between the UK and the EU.
He said: "All businesses are currently operating in extremely challenging circumstances, but it is nevertheless vital that they prepare immediately for our new relationship with the EU, outside of the single market and customs union. Unless business takes action now, there is a risk that their operations will be interrupted.
"Businesses will play an essential role in ensuring a smooth end to the transition period and the UK government will be there to support them as we embark on a new start for Wales and the UK."