The European Commission said on Wednesday it had opened three in-depth investigations into tax decisions affecting Apple, Starbucks and Fiat Finance and Trade in Ireland, the Netherlands, and Luxembourg respectively.
The probes focus on whether decisions by authorities in the three European Union member states about corporate tax to be paid by the three companies comply with state aid rules.
Corporate tax avoidance has risen to the top of the international political agenda in recent years amid reports of how companies like Apple and Google use convoluted structures to slash their tax bills.
The EU said its investigation follows reports some companies have received significant tax reductions through rulings by national authorities.
Starbucks told a UK parliamentary investigation in 2012 that it received a tax deal in the Netherlands which allowed it to enjoy a "very low" tax rate, while a U.S. Senate probe last year showed that Apple had sheltered tens of billions of dollars in profits from tax by using Irish companies that had no tax residence anywhere.
Tax rulings are used in particular to confirm transfer pricing arrangements, covering prices charged for transactions between various parts of the same group of companies.
Apple said it has not received any selective tax treatment from the Irish authorities. Fiat and Starbucks were not immediately available for comment