WASHINGTON — Orders for long-lasting U.S. factory goods declined for the second straight month in May, as demand for cars, metal products and aircraft fell.

The U.S. Commerce Department said Wednesday durable goods orders — items meant to last at least three years, from washing machines to tractors — dropped 0.6 per cent last month. That followed a steeper drop of one per cent in April. A category that tracks business investment slipped 0.2 per cent, after a healthy gain of 2.3 per cent in April.

Even with May's decline, factory output has expanded this year. Businesses and consumers are increasingly confident and are spending more.

Still, American manufacturers are in the centre of a growing storm over international trade that may be starting to weigh output. The Trump administration and Europe, China and Mexico have slapped punitive tariffs on each other's factory goods.

The U.S. has imposed stiff duties on steel and aluminum, and is preparing to place 25-per-cent tariffs on US$50 billion of imports from China. Europe, Mexico and China have already imposed retaliatory tariffs and China is threatening to do more.

The duties have raised the prices of steel and aluminum in the United States, likely disrupting industrial supply chains. Orders for raw metals fell 0.4 per cent in May. That followed large gains in April and March, which may have reflected an effort by many manufacturers to stock up on steel and aluminum before the full force of the tariffs hit.

Orders for fabricated metal parts and components also dropped, falling 1.2 per cent, following two months of strong increases.

Demand for computers, electrical equipment and appliances, and cars also declined. Industrial machinery and communications equipment were the only categories to show increases.

April's figures were revised much higher, offsetting some of the impact of May's decline. The category tracking business investment was initially estimated to have increased one per cent, but was boosted to show a 2.3-per-cent gain.