Hopes of securing a post-Brexit U.S.-U.K. trade deal have come under threat in the first day of talks amid concerns over chlorinated chicken imports.

Britain’s International Trade Secretary Liam Fox has insisted that the issue of poultry imports is “a detail of the very end stage of one sector” but British campaigners insist that a proposed bilateral trade deal with the U.S. would lower British food standards.

Fox is currently in Washington for the second of two-day trade talks with U.S. Commerce Secretary Wilbur Ross in which they aim to lay establish a continuity agreement that will allow the two countries to continue trading after Brexit. They also hope to “lay the ground work” for a potential future free trade agreement, Fox said in a press statement Monday, though cannot sign a deal until the U.K. leaves the EU in March 2019.

U.S. farmers have insisted that any future deal with the U.K. must include agriculture but British campaigners argue that it would hurt farming standards and leave consumers faced with imports of chlorine washed chicken and hormone-fed beef.

In the U.S. it is legal to wash chicken carcasses in chlorinated water: producers and regulators in the U.S. argue it reduced the spread of contamination. Such items are banned in the EU on health grounds and concerns that it could be used by unscrupulous producers to make meat appear fresher.

Once the U.K. leaves the EU it will be free to decide whether to retain the EU’s ban or lift it and accept U.S. food standards. These differing views on the issue are partly what caused the U.S. and the EU to fail to agree on a transatlantic trade and investment partnership (TTIP) last year.

President Donald Trump, who has long advocated striking a deal with the U.K., tweeted Tuesday that “protectionist” EU rules were preventing a deal and the creation of new jobs.

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Though industry bodies have said EU regulations should remain in place. The British Poultry Council slammed the notion of importing chlorine-washed chickens as part of a “makeweight in trade negotiations with the U.S.”

“The U.K. poultry meat industry stands committed to feeding the nation with nutritious food and any compromise on standards will not be tolerated. A secure post-Brexit deal must be about Britain’s future food security and safety. This is a matter of our reputation on the global stage,” it said in a press note.

During a joint press conference with Ross Monday, Fox dismissed critics, saying that the British media was “obsessed” with chlorine-washed chickens and risked undermining plans to achieve a free trade agreement with the U.S.

The spat comes against the backdrop of divided public opinion over the future of the U.K.’s agriculture industry. Pro-Brexit farmers argue that outside the EU there will be less arbitrary regulations and no need to subsidize farmland in other countries. Meanwhile advocates of the union insist it maintains high standards and prevents farmers being undercut by cheaper producers.

As the world’s largest beef producer, supplying one-fifth of the beef eaten around the world, the U.S. would likely plug the gap left by the EU. However, critics have argued that this would leave British farmers at risk of being undercut by larger, and typically cheaper, producers.

The U.K’s shadow trade secretary Barry Gardiner criticized Fox Monday, saying “never trust a Fox in your hen coop.”

“By arguing the case for chlorine-washed chicken, Liam Fox shows he is ready to abandon British poultry farmers in favour of cheap U.S. imports that do not meet our sanitary or animal welfare standards,” he said.

“The U.S. is our biggest trading partner outside of the EU and accounts for 17 percent of British exports. We want to see that figure grow and every effort must be made to support British exporters and reduce unnecessary barriers to trade, but never at the expense of the interests of British consumers and producers.”

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