The European Union may join Japan in a complaint against Chinese steel duties, petitioning the World Trade Organization for relief, EU sources told Reuters.

The sources said the complaint against Chinese duties on steel is separate from a dispute between China and the EU over fresh European tariffs on Chinese solar panels and a Chinese investigation into alleged dumping of European wine.

The EU complaint could come as soon as Thursday or Friday this week, according to the sources.

According to WTO rules, tariffs and other trade barriers cannot be imposed “arbitrarily” or as a form of retaliation, as some critics have charged China with doing.

Japan filed a complaint against Chinese duties on stainless steel seamless tubes from Japan in December 2012, requesting arbitration from the WTO and an overturning of the Chinese duties.

Japanese companies Kobe Steel Ltd. (TYO:5406) and Nippon Steel & Sumitomo Metal Corp (TYO:5401) were among companies that contributed to a steel tube export trade worth $69 million in 2011, according to Reuters.

The EU requested to join those discussions in early 2013 but hadn’t yet filed a similar formal complaint. Those discussions ultimately failed.

The U.S. won in a similar complaint filed against Chinese duties on a different type of steel in October 2012, even after China appealed the case to the WTO.

The EU, India, Korea, Russia and the U.S. have all expressed a formal interest in the Japan WTO complaint. 

EU trade spokesman John Clancy didn’t immediately return a request for comment.