The United States and the Union each follow elaborate, quasi-judicial procedures for anti-dumping and anti-subsidy cases, taking voluminous statements from affected companies before acting, and following detailed rules for setting any tariffs. China’s methods for assessing trade penalties are relatively mysterious, and have been the subject of periodic European and American criticism.

The Union is preparing to start the investigation in response to a complaint filed by a coalition of about 20 European companies led by SolarWorld, a German maker of solar panels. SolarWorld, which also has operations in Oregon, had previously set up a coalition of solar panel producers in the United States that used a legal filing to force the Commerce Department to file the cases there.

Chen Huiqing, deputy director for solar products at the China Chamber of Commerce for Import and Export of Machinery and Electronic Products, said at an industry conference in Guangzhou two weeks ago that the Chinese industry had sent a team of representatives to Brussels in one last bid to talk European officials out of starting a trade case. She warned that Chinese solar panel manufacturers already faced declining profit margins, shortages of capital and weakening foreign demand.

Chinese companies played a tiny role in the global solar power industry until five years ago, when they began a surge that has now brought them two-thirds of the global market. That rapid growth has been accompanied by a steep plunge in wholesale prices for solar panels, which have dropped by up to three-quarters in the past four years.

Retail prices have fallen much more slowly, as the bulk of the cost of a solar panel system lies in installation, and those costs have not fallen nearly as fast.

Chinese industry officials and regulators have periodically denied allegations that they are selling solar panels below cost in foreign markets, insisting that their huge investments in big new factories have brought down costs. But big Chinese solar companies have been posting heavy losses, particularly in the second quarter.

Frank Haugwitz, a solar industry consultant based in Beijing, said that if the Union imposed tariffs, it would be a serious blow to a Chinese industry already suffering from overcapacity. But the Chinese government is strongly committed to having a large solar panel industry, and is starting to use subsidies to expand the modest domestic market for solar panels.