Farmers have raised the alarm that Britain could be flooded with meat from countries with weaker welfare standards under a new trade deal.
Tory ministers are set within days to reach an agreement in principle for the country to join the Trans-Pacific trading bloc, which includes Canada and Mexico.
But the issue of access to the UK beef and pork markets is understood to be one of the key issues still under negotiation.
The National Farmers' Union is demanding reassurance that British farmers and growers’ businesses will not be damaged.
Talks with the 11-nation group - whose members also include New Zealand, Australia, Singapore, Japan, Chile, Vietnam and Malaysia - have been going on since 2021.
Environment Secretary Therese Coffey is understood to be pushing to limit how much meat can be shipped to the UK under the deal.
Concerns have previously been raised over Canada wanting Britain to get rid of a ban on hormone-treated beef.
There are now fears that lower animal welfare standards in countries in the Trans-Pacific trade bloc could mean members are able to undercut UK farmers.
NFU President Minette Batters said: “Joining the CPTPP (the Comprehensive and Progressive Agreement for Trans-Pacific Partnership). could provide some good opportunities to get more fantastic British food on plates overseas, but we are concerned that the cost will be heavily borne by our beef, poultry and pork farmers.
“As we examine the details of any agreement, we will want to see evidence that our negotiators have not opened up our markets to unmanageable volumes of agricultural produce that will damage our farmers and growers’ businesses.”
A Government spokesperson said: “We will not sign a deal that forces the UK to compromise its high food safety, environmental protection and animal welfare standards.
“Joining CPTPP means 99 per cent of UK goods exports could be eligible for tariff-free trade to a market of 500 million customers.”
Ms Coffey was last week branded "Calamity Coffey" by her Labour counterpart after an "outrageous display" which saw her booed at an NFU conference.
Ms Coffey was criticised after a dismal display at the convention which saw her say egg shortages were not caused by "market failure" and telling farmers "we can't control the weather in Spain”.
Shadow environment secretary Jim McMahon told the Commons: "Although there might have been differences about the impact and the scale of the impact, there was consensus. And the consensus was that the Environment Secretary had a pretty bad day at the office.
"Some describe it as a slow motion tractor crash; 'Calamity Coffey'. But either way and joking aside, it was an insult to the very foundation of our food security and hardworking British farmers."
He added: "Will the Environment Secretary, not the farming minister, use this opportunity to apologise for the outrageous display at the NFU conference in Birmingham yesterday?"
Environment minister Mark Spencer stepped in, telling Mr McMahon that Ms Coffey couldn't answer due to parliamentary procedure.
He added there had been "robust exchanges" with NFU members, adding that ministers would "continue to work with the NFU" and other groups who represent farmers.
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