US warned auto tariffs will raise prices

US automakers are warning that the Trump administration's plan to impose 25 per cent tariffs on imported cars and parts will raise prices and hurt the sector.

A group representing major automakers will tell the US Commerce Department that imposing tariffs of 25 per cent on imported cars and parts would raise the price of US vehicles by $US83 billion ($A112 billion) annually and cost hundreds of thousands of jobs.

The Alliance of Automobile Manufacturers, whose members include General Motors, Volkswagen and Toyota Motor Corp, said it plans to issue the warning at a public hearing on Thursday.

"Higher auto tariffs will harm American families and workers, along with the economy" and "would raise the price of an imported car nearly $US6,000 and the price of a US-built car by $US2,000," the group said.

The European Union, Japan, Canada, Mexico, along with many automotive trade groups, Volkswagen, and the United Auto Workers union are among those scheduled to testify at the hearing.

The Trump administration in May launched an investigation into whether imported vehicles and parts pose a national security threat and US President Donald Trump has repeatedly said he would quickly impose tariffs of 20 or 25 per cent.

The Commerce Department says it has made no decisions and aims to complete the investigation "within a couple months."

The auto industry has banded together in a full-scale campaign to oppose the tariffs, with companies warning of slower auto sales due to higher prices, lost jobs as well as reduced spending on self-driving cars.

Toyota North America Chief Executive Jim Lentz told company dealers in an email seen by Reuters that "Toyota and the entire auto industry is facing a very dangerous public policy threat - a potential 25 per cent tariff on all imported autos and auto parts - and we need YOU to help us win this battle!"

John Bozzella, who heads the Association of Global Automakers, which represents Honda, Hyundai and other foreign automakers, said that Commerce "so far has been unable to outline any theory explaining how the commercial production of cars and trucks is connected to US national security."

Many automakers opted not to testify at the hearing because they believe Trump cannot be swayed from his decision to impose the tariffs.

Some administration officials have suggested that his threats are a tactic to win concessions in trade talks, including North American Free Trade Agreement renegotiations.