The European Union's trade chief vowed Tuesday to tax Chinese solar panels next month in the largest EU commercial dispute of its kind, while urging China's exporters to boost prices in return for an eventual end to the tariffs.

EU Trade Commissioner Karel De Gucht defended a proposal to impose provisional duties on Chinese manufacturers of solar panels for allegedly selling them in the 27-nation EU below cost, a practice known as dumping.

The EU levies, due by June 6, would be the preliminary outcome of a dumping inquiry that the European Commission opened in September and that German Chancellor Angela Merkel said Sunday shouldn't lead to permanent duties against China. The commission is the 27-nation EU's regulatory arm.