Chamber of Commerce President Tom Donohue said Tuesday that the U.S. has run out of workers and needs more immigration to ensure that that the economy remains strong. He also warned that Congress would face a "big time brawl" with the nation's leading business trade group if it doesn't pass immigration reform that gives existing legal immigrants a pathway to citizenship. [There simply aren't enough people - out of]

"The United States is fundamentally out of people," Donohue said in a speech at the Chamber's headquarters. "I used to run the American Trucking Association. There is demand for 300,000 long-haul truck drivers in this country ... and the ability to get them is shrinking very quickly, and we can find 15 other industries where this is going on."

He added: "Immigrants have long been a vital part of our economy, and they can help fill those gaps now.... Our nation must continue to attract and welcome the world's most industrious and innovative people and finally fix our broken immigration system."

The U.S. unemployment rate is currently 3.7 percent, according to federal statistics, a 49-year low.

Donohue's comments come as the Trump administration is ratcheting up its opposition to illegal immigration by deploying 5,200 soldiers to the U.S.-Mexico border to prevent thousands of Central American migrants from crossing.

The Chamber has long supported relatively open immigration policies, viewing immigrants as resources that boost the economy overall. It has avoided direct confrontation with the Trump administration over the issue, instead hoping it could broker a reform deal with Congress and other stakeholders. Donohue reiterated that stance Tuesday.

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"I'll be the first to admit our current political climate makes that easier said than done, but necessity is the mother of invention, and eventually, it will be done," he said. "I think there is an opportunity to do it in the next few years for a number of reasons. One, the president is determined to secure the border. Two, 1 million immigrants working legally [under federal programs] could be removed from the workforce if we cannot get Congress to act and protect their interests."

He added that costing business those workers will result in "a big-time brawl in this [Chamber headquarters] building. You can write that down."

A reform deal would have to include the ability of employers to hire workers "at all skill levels," an updated E-Verify system, and the ability of existing legal immigrants to earn citizenship.