The Obama administration is considering an expansion of duties on Chinese solar products that has triggered complaints from a South Korean parts supplier that says it would be hurt.

The plan calls for the United States Commerce Department to impose tariffs on all solar panels assembled in China, regardless of the source of their component cells. Currently, $1.5 billion worth of panels with cells made in China are subject to a duty, and many companies shifted production of the cells to other nations in response.

The proposal highlights the challenge of applying US trade penalties on products in a far-flung, global supply chain.