The U.S. is stepping up its effort to convince the European Commission to refrain from hitting Apple Inc. with a demand for possibly billions of euros in underpaid taxes.

In a white paper released Wednesday, the Treasury Department in Washington said the Brussels-based commission is taking on the role of a "supra-national tax authority" that has the scope to threaten global tax reform deals.

"This shift in approach appears to expand the role of the commission's Directorate-General for Competition" that goes "beyond enforcement of competition and state aid law," the Treasury wrote in the paper. "The cases cited by the commission do not give taxpayers prior notice that the commission would interpret its powers in this way or that selectivity would no longer be a meaningful precondition to a finding of state aid."