The Trump administration's tough trade policies could stymie economic growth — and threaten as many as 2.6 million jobs, the U.S. Chamber of Commerce's top official is reportedly warning.

The Wall Street Journal reported Thursday a grim memo from the chamber's chief executive, Tom Donahue, followed news President Donald Trump would make good on threats to apply tariffs to steel and aluminum imports from Canada, Mexico, and the European Union.

"A growing list of tariffs proposed or imposed by our government, as well as the continued uncertainty over the future of [the North American Free Trade Agreement], threatens to undermine the economic progress we have made," Donohue wrote in the memo, the Journal reported.

Domestic steel and aluminum producers support the tariffs on metals, the United Auto Workers and United Steelworkers unions are supporting the administration's examination of whether car or auto-part imports should face barriers under the banner of national security, the Journal reported.

Unions and other groups also question the economic estimates that business groups have linked to trade-policy changes, the Journal reported.

But GOP lawmakers are siding with Donahue's concerns, the Journal reported.

"The current approach — and the obvious retaliation that will occur in response — poses a serious risk of raising barriers and reducing Americans' access to vital global markets," Donohue wrote in the memo, the Journal reported. "Our businesses will lose customers, workers will lose jobs, and American consumers will lose family income through higher taxes and higher prices."

Donohue warned withdrawing from NAFTA could cost as many as 1.8 million U.S. jobs in the first year, according to the Journal, while he also warned tariffs against China and the steel and aluminum tariffs, among others, could cost hundreds of thousands more jobs.

Economists also sounded the alarm, saying the measures, combined with retaliation, could generate significant losses — and U.S. stocks fell Thursday.

But Commerce Secretary Wilbur Ross argued current tariffs and planned retaliation will have a small effect on consumer prices, including those on metal products, and a small impact on the U.S. economy.

"The beer, soft drink, and soup cans — it's all a fraction of a penny on each of those," Ross told CNBC. "In terms of the automobile, it's also a fraction of 1 percent, and for the economy overall, it's a very small fraction of 1 percent."