The investigations centre on Luxembourg's tax rulings for online retailer Amazon and carmaker Fiat Chrysler, as well as coffee chain Starbucks' deal with the Netherlands and iPhone maker Apple's Irish arrangements, and whether the companies are paying a fair share of tax.

"The cases are advancing very well. I expect decisions to be taken in the not so distant future," Gert-Jan Koopman, deputy director general at the Commission, told a conference.

European Competition Commissioner Margrethe Vestager said last month she would not be able to meet a second quarter deadline as targeted and would not set another deadline for her decision.

The global financial crisis and cash-strapped governments have spurred a crackdown on tax avoidance and prompted complaints that deals which help companies cut their tax bills to a minimal level may give them an unfair advantage in breach of EU rules.

The European Commission is also investigating Belgium's tax arrangements for multinationals and on Thursday it opened a formal antitrust investigation into Amazon's e-book business.

By Foo Yun Chee