Automakers ship billions of dollars' worth of vehicles and parts across the U.S. borders with Canada and Mexico every day. President Donald Trump's plan for 25% tariffs on imports from those countries could severely disrupt those operations.

On Monday, hours after his inauguration, Trump said he planned to impose the tariffs beginning February 1. Now the question is whether he will follow through - or what terms might keep him from doing so.

"Most people in the industry are waiting to see what happens and to see what the administration is looking for from Canada and Mexico," Mark Wakefield, global automotive market lead at AlixPartners, a consulting firm, said Tuesday. "For now they assume this is more a negotiating chip than it is something that's really going to happen."

General Motors and Ford Motor declined to comment on the matter. Both companies produce significant numbers of vehicles and components in Canada and in Mexico, and both ship vehicles and parts from plants in the United States into those countries.

In theory, tariffs would force automakers to move production to the United States and ultimately create more jobs. But re-engineering cross-border supply chains would be extremely difficult and costly.

And in the short run, tariffs on vehicles and parts from Canada or Mexico would lead to higher prices at dealerships and lower demand for cars. Rather than protecting U.S. autoworkers, as Trump has promised, tariffs would lead to job losses because automakers would cut their workforces to compensate for slumping sales, analysts said.

"Ultimately what happens is you sell less units and therefore you need less people," said Simon Geale, an executive vice president at Proxima, a consulting firm that focuses on supply chains.

The impact of tariffs would depend on how steep they are and how they are applied. A 25% tariff on a USD 5 part would, by itself, not be that big a deal. But a 25% tariff on a fully assembled vehicle made in Mexico would almost immediately force a 25% increase in the sticker price of the same vehicle.

"Tariffs will inflate car prices that many potential buyers already think are too high," said Erik Gordon, a business professor at the University of Michigan.