We need a trade policy that safeguards our farmers and British food production from the damaging impact of importing food that would be illegal to produce here.
Farmers are calling for a trade policy that protects high UK environmental and animal welfare standards for food as legislation comes to Parliament.
The National Farmers' Union is urging MPs to ask how the Government will honour its manifesto pledge that environmental and animal welfare standards for food produced in the UK will not be undermined in future trade policy.
And the farming body is continuing to call for a new "trade, food and farming standards commission" to review policy and come up with measures to promote free trade while holding all food imports to UK standards.
Farmers and environmental groups fear future trade deals could allow imports of cheap food produced to standards which would be illegal here, undercutting produce grown and reared in the UK in ways that look after nature and animal welfare.
The call comes as a new Trade Bill is being debated in the Commons and after efforts by MPs to amend the Agriculture Bill to guarantee post-Brexit food imports will match the UK's food and environmental standards failed last week.
NFU president Minette Batters, who has written to all MPs, said the UK had the potential to be at the very top on the global stage when it came to food and farming.
"But we need a trade policy that safeguards our farmers and British food production from the damaging impact of importing food that would be illegal to produce here," she said.
"Failure to do this would undermine our values of animal welfare, environmental protection and food safety, all of which are incredibly important to the public."
MPs had said the standards of imported food was an issue for the Trade Bill rather than the Agriculture Bill, Ms Batters said, and she hoped to see it addressed as the legislation on trade was debated.
"Our trade policy must reflect our moral responsibilities to the planet and the people and creatures that live on it - protecting our natural environment, caring for our farmed animals, and working toward a more sustainable, climate-friendly way of farming and food production.
"These are issues that cannot be wished away or presumed dealt with by brief pledges in a manifesto or verbal assurances in media interviews," she warned.
And she urged MPs to "speak up for British farming" by asking for a commission that will protect UK food from sub-standard imports and for more parliamentary scrutiny over future trade deals.
"We are at a make or break moment for British farming. We have the chance to become a global leader in climate-friendly farming, and neither farmers nor the public want to see that ambition fall by the wayside because our trade policy does not hold food imports to the same standards as are expected of our own farmers," she said.
A spokeswoman for the Department of International Trade said: "The UK is renowned for its high environmental, food safety and animal welfare standards. And we will safeguard our agriculture sector - we've just announced a tariff policy which maintains tariffs on key agricultural products such as lamb, beef, and poultry.
"We have been clear that in all of our trade negotiations - including with the US in our first round of negotiations - that we will not undermine our high domestic environmental protection, animal welfare and food safety standards by ensuring in any agreement British farmers are always able to compete."
Emily Beament is the PA environment correspondent.