Washington has proposed an extra 12.5% tariff on Swiss exports as part of a sweeping new offensive against 60 economies.
The US Trade Representative says the measure targets countries the administration accuses of failing to block imports made with forced labour - Switzerland, China, the EU, Japan, India and Mexico are all named.
The proposal is the Trump administration's attempt to find fresh legal cover after the Supreme Court struck down its earlier tariffs in February.
If implemented, Swiss exporters would face a new cost on goods sold into the United States, with semiconductors, beef and coffee among the few categories exempted.
A public comment window runs until 6 July, with hearings opening the next day in Washington.
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