EU officials opened an investigation into the tax affairs of major multinationals in Belgium on Tuesday.
The probe focuses on so-called “excess profit” tax rulings and whether they amount to state aid.
They allow companies to reduce their corporate tax liability due to “excess profits” they claim are the result of being part of a multinational group.
EU’s Competition Commissioner Margrethe Vestager said “certain multinationals end up paying taxes only a part of their taxable profits in Belgium without being justified under taxation principles.”
The European Commission declined to comment on how many companies are involved.
It means the EU has now opened five state aid investigations related to corporate tax.
The subject has been back in the spotlight after it emerged more than 300 corporations had brokered favourable tax deals with Luxembourg.