WASHINGTON — The White House's on-again, off-again tariffs are heightening uncertainty for U.S. companies that buy steel and aluminum and the foreign companies that supply them.

And major American allies, from Europe to Canada and Mexico, are signaling increasing resentment.

Delivering its second reprieve for steel and aluminum imports, the Trump administration late Monday postponed the tariffs that had been set to take effect Tuesday. But it decided to limit the delay to 30 days. After that, no one knows what the administration will do.

"It's nice to have a little breather," said John McDonald, an executive at Trans-Matic Manufacturing, a supplier of precision metal components in Nashville, Tennessee, which buys $16.5 million in steel annually, some from Finland, the Netherlands, Russia and Taiwan. But "the uncertainty is going to continue."