The former environment secretary said she was worried about how a post-Brexit deal with the Americans would impact rural communities across the UK. She said any negative impact on famers would have a ripple effect on the rural economy and the union “because of the significance of livestock farming in Northern Ireland, Scotland and Wales”.
Ms Villiers lost her spot in Boris Johnson’s Cabinet to George Eustice in February’s reshuffle.
Mr Eustice is thought to have clashed with Trade Secretary Liz Truss over the terms of a UK-US deal.
Ms Villiers told The Daily Telegraph she had “great fears” about “unfettered competition between domestic farmers and US imports”.
And she voiced concern over the situation British farmers would find themselves in trying to compete with cheap meat imports.
A number of fears have been raised since President Donald Trump said he wanted a big trade deal with the UK after it had left the European Union.
Critics have pointed to lower food standards stateside, including chlorine washing of chicken.
And the prospect of packs of hormone-injected beef landing in British supermarkets has also caused worries.
Opposition MPs have called on the Government to enshrine guarantees into the Agricultural Bill.
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If no action is taken, she warned, the Americans would push for “complete liberalisation of trade in food without any kind of preconditions”.
She added: “We have legislated to prevent the importation of chicken that has been washed in chlorine or other substances, and I very much hope that stays on statute book.
“But I would imagine there will be significant pressure from the US to lift that restriction because they have had a longstanding dispute with the EU as to justification of that as a restriction.”
Ms Truss has in the past offered assurances to farmers.
She said the UK would not sign a deal with the US if it “does not benefit every sector of UK agriculture”.
Meanwhile negotiations on a trade deal with the EU continue to drag on with little progress in sight.
Both sides have in recent weeks clashed over a number of key issues.
Fishing is one area where Brussels and Britain have so far failed to see eye-to-eye.
The EU is demanding continued access to British waters after the Brexit transition period has ended on December 31 – something which the UK has said is not possible.