The European Union said it will require Starbucks and Fiat Chrysler to pay tens of millions of euros in back taxes after ruling that the companies benefited from illegal tax deals in an unprecedented decision that risks overturning thousands of corporate tax structures across Europe. The European Commission, the EU's executive arm, said Wednesday that tax deals granted to Starbucks in the Netherlands and Fiat in Luxembourg amounted to illegal state subsidies that must be repaid.