Shares in two major carmakers tumbled after they warned that changes to trade policies were hurting performance.
General Motors said it expected a hit of about $1bn (£760m) due largely to higher steel and aluminium prices caused by new US metals tariffs.
Shares dropped by more than 7% after the firm revised its outlook.
Fiat-Chrysler shares were about 15% lower, after it said sales in China had fallen as buyers postponed purchases in anticipation of lower tariffs.
The warnings give an insight into how shifting trade policies are affecting carmakers and other manufacturers.
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Executives at Fiat-Chrysler said fixed price contracts have helped to shield it from some of the impact of higher metals prices, but it expected those costs to rise in 2019.
General Motors said metals costs this year would be about $600m-$700m higher than expected. The firm has also been affected by currency declines in Brazil and Argentina.
The changes prompted the firm to reduce its profit forecast for 2018.
General Motors chief executive Mary Barra said the firm had anticipated higher costs this year, but “the challenge has become significantly greater than we expected”.
‘Uncertain and volatile environment’
She said the firm had been in frequent contact with the White House about how trade policies would affect its business.
In addition to the metals tariffs, the Trump administration is considering placing new duties on foreign vehicles and car parts.
Carmakers are also grappling with questions about negotiations to do with the North American Free Trade Agreement (Nafta).
The firm is also worried that trade tensions could eventually put buyers in China off American brands. China is GM’s biggest market after North America.
“We are in a very uncertain and volatile environment at this time,” said GM chief financial officer Chuck Stevens.
The forecasts came amid disappointing quarterly results.
Fiat Chrysler revenue increased 4% in the quarter to almost $29bn, but profits tumbled by 35%.
It saw sales, especially of Maseratis, slump 35% as customers in China waited for lower tariffs on foreign vehicles to come into effect.
The firm expects those to rebound, but will be grappling with the country’s new emissions rules.
Sales and revenue at GM were about $36.8bn, down almost 1% in the three months to the end of June, compared with the same period last year.
The firm said profit was about $2.4bn, down about 2.8% year-on-year.
The results came despite gains in the US, where the number of vehicles sold to dealerships increased by 4.6% amid increased demand for pickup trucks.