WASHINGTON (Reuters) -President Donald Trump said on Thursday his administration would impose tariffs on semiconductor imports from companies not shifting production to the U.S., speaking ahead of a dinner with major technology company CEOs.

Since returning to office in January, Trump's threat of tariffs has alienated trading partners, stirred volatility in financial markets and fueled global economic uncertainty.

"Yeah, I have discussed it with the people here. Chips and semiconductors - we will be putting tariffs on companies that aren't coming in. We will be putting a tariff very shortly," Trump said without giving an exact time or rate.

"We will be putting a very substantial tariff, not that high, but fairly substantial tariff with the understanding that if they come into the country, if they are coming in, building, planning to come in, there will not be a tariff," Trump told reporters.

Trump has made tariffs a pillar of U.S. foreign policy, using them to exert political pressure and renegotiate trade deals and extract concessions from countries and companies that export goods to the U.S.

"If they are not coming in, there is a tariff," Trump said in his comments on semiconductors.

"Like, I would say (Apple CEO) Tim Cook would be in pretty good shape," he added, as Cook sat across the table.

iPhone maker Apple recently raised its total domestic investment commitment in the U.S. to $600 billion over the next four years as tech leaders have warmed up to Trump in his second term.

Trump said last month that the United States would impose a tariff of about 100% on imports of semiconductors but it will not apply to companies that are manufacturing in the U.S. or have committed to do so.

Taiwanese chip giant TSMC and South Korea's Samsung Electronics and SK Hynix have announced investments in chip manufacturing in the United States.

Trump has faced legal pushback in his use of tariffs. His administration has asked the U.S. Supreme Court to swiftly hear a bid to preserve his sweeping tariffs pursued under a 1977 law meant for emergencies after a lower court invalidated most of the levies that have been central to his economic and trade agenda.