U.S. solar panel imports remain under pressure as trade disputes threaten to choke off equipment supplies for project developers.

The number of shipping containers delivering solar panels to American ports during the fourth quarter of 2021 was up slightly from the prior quarter but down 7% from a year earlier.

Imports have fallen sharply since mid-2021 as the U.S. started detaining panels linked to alleged labor abuses in China, and domestic manufacturers began pushing the U.S. Commerce Department to extend tariffs on Chinese products to countries in Southeast Asia, which have become the main suppliers to America's solar market in recent years.

The latest threat came Feb. 8, when Auxin Solar Inc. asked the Commerce Department to investigate whether Chinese companies have shifted solar cell and panel production to Malaysia, Thailand, Vietnam and Cambodia in order to avoid paying U.S. tariffs.

Tariff proponents have said their interests align with the Biden administration's goal to boost domestic manufacturing, adding that solar supply chains would shift to continue serving the U.S. market if the government levies new import taxes.

Their opponents disagree, noting that if the Commerce Department sides with Auxin, tariffs could be applied retroactively to shipments from a group of countries that accounted for more than 85% of U.S. solar panel imports during the final three months of 2021.

"The reason why this [case] is so critical is [because of] what this product is — it's a product that this administration is devoted to using to fighting climate change," Matthew Nicely, a partner at Akin Gump Strauss Hauer & Feld LLP and lawyer for the Solar Energy Industries Association, which opposes new trade tariffs, said on an investor call Feb. 15. "And the mere initiation of it is going to chill trade."

The Chinese Embassy in Washington did not respond to a message seeking comment. China denies committing human rights abuses.