(Reuters) – A U.S. solar industry group warned on Wednesday that tariffs on imported panels from three Asian countries would jeopardize about 20% of the solar capacity the nation is expected to install over the next two years.

Commerce Department will decide whether or not to open a trade probe into modules and solar cells from Thailand, Vietnam, and Malaysia by September end. The Solar Energy Industries Association (SEIA), a trade association, stated that these countries represent 80% in all imports of solar panels into the United States.

The SEIA wrote to Gina Raimondo, Commerce Secretary. It stated that the tariffs – which were proposed last month by an anonymous group domestic manufacturers – would have devastating effects on the sector’s growth.

The letter was signed by almost 200 solar companies. It stated that tariffs “would be very detrimental to our companies as well as the entire American industry.”

According to the SEIA, tariffs could affect 18 gigawatts of solar projects (GW) by 2023. This is enough power for approximately 3.4 million households.

The Commerce Department was asked last month by the American Solar Manufacturers Against Chinese Circumvention to look into unfair imports from three of the countries. The group accuses producers of moving manufacturing to these countries to dodge U.S. countervailing and antidumping duties.

Because they were afraid of reprisals in the marketplace, companies that requested the tariffs and probe wouldn’t identify themselves.

This petition is just the latest effort by small U.S. manufacturers to find trade solutions to make their panels competitive with the cheaper Asian ones that have dominated the market. Since the industry’s infancy, SEIA has been opposed to tariffs on imports of solar panels.