Relief has given way to anxiety in Switzerland over the concessions made to spare the small Alpine nation from US President Donald Trump's threat of a stark 39 percent tariff.

Many details of the agreement Bern struck last week to slash the levy to 15 percent, on par with the surrounding European Union, have yet to see the light of day.

Businesses hailed the deal as averting potential disaster for the export-driven Swiss economy.

But others fear the fine print will include relaxing rules on the import of American food, including hormone-fed cattle and the chlorinated chicken which has become a bete noire of European critics of US big agriculture.

Switzerland's powerful farming lobby has waded into the debate, with farmers' union Uniterre rejecting any imports of chlorinated chicken and

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