EU tax probe widened to Belgium
The European Commission has widened its corporate tax probe to include Belgium's rules on so-called "excess profit".
It is the latest European Union member state to have its tax regime put under the spotlight.
The Commission is investigating whether the tax regimes of certain EU nations amounts to state aid.
It said Belgium often made tax deals with firms that moved "a substantial part of their business" to the country.
US corporations, including Apple, Starbucks and Amazon have also been caught up in the investigation for what the Commissions calls their "aggressive tax planning" strategies.
Under European Union (EU) state aid rules member states are not allowed to grant companies selective tax advantages that distort competition.
But the Commission said that, on the face of it, Belgium's excess profits tax regime did just that.
Commissioner Margrethe Vestager in charge of competition policy said: "The Belgian 'excess profit' tax system appears to grant substantial tax reductions only to certain multinational companies that would not be available to stand-alone companies.
"If our concerns are confirmed, this generalised scheme would be a serious distortion of competition unduly benefitting a selected number of multinationals. As part of our efforts to ensure that all companies pay their fair share of tax, we have to investigate this further."
The Commission said Belgium's tax arrangements meant as much as 90% of the profits a multinational corporation made in the country could be deducted from the its corporation tax bill, although more typically, the tax break applied was 50%.
The Commission added the Belgian tax regime, as it stood, appeared to imply those profits would not exist were the subsidiary not part of a multinational group, benefitting from the shared resources that go with being part of a large corporation, such as a global human resources department or IT system.
In order for the deductions to be applied, a company needed to reach an agreement with the Belgian government first.
The Commission has been investigating the tax regimes of certain member states since June 2013 and widened the investigation to include all member states at the end of last year.
Eight months ago the Commission launched formal investigations into the tax paid by Apple in Ireland, Starbucks in the Netherlands and Fiat Finance in Luxembourg.
It launched a further investigation into Amazon's tax dealings in Luxembourg in October.
The investigations into Luxembourg's tax regime led to calls for European Commission President Jean-Claude Juncker to be investigated over allegations he encouraged tax avoidance when he was prime minister of the country.
Mr Juncker has denied the claims.