WASHINGTON — A flood of imported solar equipment has seriously hurt American companies, the International Trade Commission ruled on Friday, setting up a major test of President Trump’s willingness to use the protectionist measures he endorsed during the campaign.

The commission will now devise a course of action to recommend to Mr. Trump by Nov. 13. Its recommendations — which the president will have broad leeway to accept, amend or reject — could include establishing tariffs or minimum prices on imported solar equipment.

The commission ruled 4-0 in a case that focused on the question of whether the financial woes of two companies, Suniva and SolarWorld Americas, were caused by their own business practices or by unfair competition, often from Chinese companies that benefit from state subsidies.

The commission determined that the domestic solar equipment industry had been harmed by imports, including those from trading partners like Mexico and South Korea, with one commissioner adding Canada to the list.