Spain's Repsol SA filed a complaint against Argentina before the International Center for Settlement of Investment Disputes (ICSID) today over its nationalization of energy company YPF SA, a source familiar with the matter told reporters.

In May the government seized 51 percent of the country's biggest oil company from Repsol, accusing the former parent company of underproduction and under-investment.

In its complaint, Repsol calls the seizure unlawful and discriminatory, according to a source who asked not to be named and who had seen a copy of the document submitted to the ICSID.

The Spanish oil major denied Argentina's charge that it neglected to invest in YPF. The takeover also sparked protests against Argentina from the European Union and other trade partners. Repsol says the 51 percent of YPF expropriated by the government is worth $10 billion.