GENEVA (Reuters) - U.S. President Donald Trump’s tax reform could bring almost $2 trillion back to the United States as U.S. firms repatriate cash piles from foreign affiliates, a U.N. report said on Monday.

A press release on tax reform in the U.S. is pictured during a press conference of the United Nations Conference on Trade and Development (UNCTAD) in Geneva, Switzerland February 5, 2018 REUTERS/Denis Balibouse

Ending the incentive to hoard cash overseas could produce a stimulus effect in the United States, and Trump has credited the tax reform with spurring a $350 billion investment plan by Apple. AAPL.O

“Now is the perfect time to bring your business, your jobs, and your investments to the United States of America,” Trump told the World Economic Forum in Davos last month.

The reform ends a system whereby companies defer tax on foreign earnings until the funds are repatriated. Instead it treats those earnings as if they were being repatriated, with an 8 percent tax on non-cash assets and a 15.5 percent tax on cash.

“This measure is widely expected to have the most significant and immediate effect on global investment patterns,” said the report by the U.N. trade and development agency UNCTAD.

Big firms had long awaited such a tax break, having last received one in the 2005 U.S. Homeland Investment Act, which brought $300 billion back from abroad, the report said.

Since then, U.S. overseas retained earnings have grown to $3.2 trillion, half of U.S.-owned foreign direct investment, with about $2 trillion in cash. Unlike in 2005, companies are not required to actually repatriate the funds.

The biggest overseas cash hoarders are in the tech sector, with Apple, Microsoft, Cisco, Alphabet and Oracle holding $530 billion, a quarter of the total, the report said. Other major cash holders are in pharmaceuticals and engineering.

Almost 40 percent of the funds are located in the United Kingdom or its Caribbean offshore territories such as the British Virgin Islands, UNCTAD said, citing data from the Bureau of Economic Analysis.

Even if the money was not invested in tangible assets, its withdrawal could still have a macroeconomic impact, said Richard Bolwijn, UNCTAD’s head of investment research.

“It’s still a part of... the external sources of finance helping to make up for savings shortfalls in developing countries,” he said.

Much of the impact depends on how other countries react, and there is still uncertainty as the details of the tax bill are clarified, and some concerns that the U.S. reforms could violate tax treaties and trade rules, the UNCTAD report said.