A Trump administration proposal to impose stiff levies on Chinese-made ships entering US ports is sowing panic in the country’s agriculture industry, with farmers saying the added cost threatens to upend exports of wheat, corn and soyabeans.

The US Trade Representative has recommended imposing fees of up to $1.5mn per port call on ships built in China or operated by companies with Chinese-built vessels, and hearings on the matter are scheduled for this week.

Exporters said that they largely stopped receiving bids on their commodity shipments from freight operators and those that remained were “very, very highly priced”. The sudden inability to sell bulk products threatens to halt their businesses, they said. Bulk grain exporter United Grain Corporation said it had already seen a 40 per cent increase in freight costs, in a letter to US trade officials asking them to reconsider.