On Sunday, Google's executive chairman Eric Schmidt defended his company, saying it had "always aspired to do the right thing", but added that "international tax law could almost certainly benefit from reform".

BBC: Apple 'among largest tax avoiders in US' - Senate committee

"These novel and unilateral theories of tax jurisdiction are both unprecedented and inconsistent with existing norms of international tax law and long-standing treaty commitments, " the groups argue in a letter to Algirdas Semeta, the EU tax commissioner.

CNN: US banks warn over planned EU 'Tobin tax'

Kaplan is a shareholder of the international law firm of Greenberg Traurig LLP and chair of its New York tax department.

FORBES: Expert View

He now teaches international tax as a part-time lecturer in the Tax LLM program at the University of Washington School of Law in Seattle.

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