Ireland allowed Apple to pay an effective corporate tax rate of 1 percent on its European profits in 2003 down to 0.005 percent in 2014, according to EU Competition Commissioner Margrethe Vestager.

“If my effective tax rate would be 0.05 percent falling to 0.005 percent — I would have felt that maybe I should have a second look at my tax bill,” she told reporters..

The U.S. Treasury Department, which has pushed back hard against the EU state-aid probes, said the commission’s actions “could threaten to undermine foreign investment, the business climate in Europe, and the important spirit of economic partnership between the U.S. and the EU.”

Apple executives have shared concerns about the company’s tax treatment overseas with officials in President Barack Obama’s administration.

Administration officials are broadly concerned that what Earnest called the EU’s “unilateral approach” doesn’t undermine coordinated efforts to prevent an “erosion of the tax base.” Also, he said, they want to ensure that any actions are fair to U.S. taxpayers and U.S. businesses.

Apple, which employs about 6,000 people in Ireland, was one of the first companies caught up in the EU’s backlash against corporate tax-avoidance. The EU, like other global regulators, has targeted firms that sidestep taxes by moving around profits and costs to wherever they are taxed most advantageously — exploiting loopholes or special deals granted by friendly governments.

Issues of a wide variation in the percent of corporate taxes charged by different nations across the global in a global economy continue unresolved.