LAST year California Solar Systems (CSS), a small installer of residential solar panels, decided to “Buy American”. It turned to Suniva, a Chinese-owned firm that makes photovoltaic panels in Georgia and Michigan, rather than use cheap imports. But according to CSS’s boss, Bastel Wardak, Suniva was unable to deliver what it promised, leading to unacceptable delays. He then tried SolarWorld, a more expensive producer in Oregon whose panels could also be marketed as “Made in the USA”. But troubles at SolarWorld’s German parent put a stop to that. Now Suniva and SolarWorld are seeking new protections from America’s International Trade Commission (ITC). On August 15th Mr Wardak was one of many to testify that the two firms did not deserve them.

The case pits American solar-cell makers against solar-panel installers. It could have big implications. Solar was the biggest source of power-generating capacity built in America last year, thanks to falling prices (see chart), but protections could push those prices up again. The ITC investigation, which makes use of a rusting bit of trade law called Section 201, is also a test of the Trump administration’s willingness to defend domestic manufacturing.

If the ITC decides by a September 22nd deadline that imports are a “substantial cause of serious injury” to the two manufacturers, it could recommend that Donald Trump adopt protective measures, such as import quotas. The president could then decide which remedy, if any, to apply. Opponents of the petition say protectionism would set America’s solar industry back five years, with higher prices clouding solar’s appeal as an alternative to natural gas. Solar installations have ground to a halt since June, after the ITC began its probe.

The ITC’s decision will hinge on whether its commissioners accept that imports are chiefly responsible for the travails of Suniva and SolarWorld. Juergen Stein, SolarWorld’s boss in America, points to a “circle of death” in the industry, with global overcapacity forcing down prices, which compels firms to produce more to gain the benefits of scale, which further lowers prices. SolarWorld and Suniva claim that imports are the main culprits: solar-panel installations in America climbed by 350% from 2012 to 2016, but imports rose by 500%.