WASHINGTON (AP) -- President Donald Trump on Wednesday will announce tariffs on auto imports, a move that the White House claims would foster domestic manufacturing but that could also put a financial squeeze on automakers that depend on global supply chains.

White House press secretary Karoline Leavitt said the tariffs would be detailed at a 4 p.m. EST news conference. Leavitt said that she would leave it to the Republican president to flesh out his plans to tax foreign-made autos and parts, which could be complicated as even U.S. automakers source their components from around the world.

Shares in General Motors have fallen roughly 1.7% in Wednesday afternoon trading. Ford's stock was down roughly 1.5%.

Trump has long said that tariffs against auto imports would be a defining policy of his presidency, betting that the costs created by the taxes would cause more production to relocate in the United States. But U.S. and foreign automakers with domestic plants still depend on Canada, Mexico and other nations for parts and finished vehicles, meaning that auto prices could increase and sales could decline as new factories take time to build.

"We are going to be doing automobiles, which you've known about for a long time," Trump said Monday. "We'll be announcing that fairly soon, over the next few days probably."

The auto tariffs are part of a broader reshaping of global relations by Trump, who plans to impose what he calls "reciprocal" taxes on April 2 that would match the tariffs, sales taxes charged by other nations.

Trump has already placed a 20% import tax on all imports from China for its role in the production of fentanyl. He similarly placed 25% tariffs on Mexico and Canada, with a lower 10% tax on Canadian energy products. Parts of the Mexico and Canada tariffs have been suspended, including the taxes on autos after automakers objected and Trump responded by giving them a 30-day reprieve that is set to expire in April.

Leavitt is one of three Trump administration officials who face a lawsuit from The Associated Press on First and Fifth Amendment grounds. The AP says the three are punishing the news agency for editorial decisions they oppose. The White House says the AP is not following an executive order to refer to the Gulf of Mexico as the Gulf of America.