EVERETT, Wash. — Hundreds of billions of dollars will return to the U.S. in the form of business investment if Congress passes tax reform, House Speaker Paul Ryan told Boeing employees Thursday.

Speaking at a town hall with employees on the aircraft manufacturer's factory floor, Ryan said tax reform would end the unusual U.S. practice of taxing all corporate profits worldwide, which would lead companies to immediately bring back $2 trillion to $3 trillion in profits they hold overseas to avoid the 35 percent corporate tax rate.

If that tax is eliminated, Ryan said, money would return, and some would be used by businesses to hire workers, build factories, and add equipment.

"How much? It's hard to say," Ryan said. But he later added that "hundreds and hundreds of billions at the very least" will return immediately.

The question of what would happen with those overseas profits is a major one in the tax debate. The prospect of bringing back their cash without paying the full tax rate is a significant reason for multinational corporations to back the tax reform effort.

Some of the money already has been reinvested overseas, in factories or workers there, and won't be returned.

Skeptics also believe that if companies are allowed to repatriate the funds without taxes or at a much lower rate, they will simply pay out the profits to shareholders in dividends or share repurchases, rather than invest in and expand their business.

In 2004, Congres passed legislation allowing companies to bring back overseas profits for the next two years subject to a special one-time low tax rate of 5.25 percent. Although companies did bring back over $300 billion in response, some research found that most of it went to shareholders rather than investment, and the legislation is generally viewed as a mistake.

Another major question is whether the accumulated funds overseas would again a one-time tax, and how much tax revenue that might raise.

Ryan's suggestion is that a large amount would be dedicated to expanding business.

The current Treasury practice of taxing worldwide profits puts U.S. businesses at a disadvantage, Ryan said, using the example of Harley-Davidson, the motorcycle company based in his home state of Wisconsin. In selling overseas, Harley faces foreign taxes and the U.S. corporate tax. In comparison, Honda doesn't face a Japanese corporate tax for U.S. sales of its Gold Wing bike, which Ryan called an "inferior competitor."