Apple may be on the hook for as much as $8 billion in taxes owing to the European Union, Bloomberg reports. A European Commission investigation which began in 2014 called into question Apple’s tax deals in Ireland, where the company’s European operations are headquartered. More recently, Apple agreed to pay $347m in back taxes to Italy after failing to declare revenue to that country’s tax authorities, instead transferring profits to its Irish subsidiary.

The European Commission has been contending that Apple’s deal in Ireland has allowed it to pay lower taxes to the Irish government by calculating its tax bill using lower operating costs in that country. Bloomberg’s analysis suggests that Apple’s foreign tax rate is about 1.8 percent, despite the company generating more than 50 percent of its revenue outside of the U.S. As a result of its findings, the European Commission may decide to enforce a tougher accounting standard that could require Apple to pay eight years of back taxes, covering $64.1 billion dollars in profit from the years 2004 to 2012, at a higher 12.5 percent tax rate. Notably, Apple is not alone in facing scrutiny from EU regulators, with other high profile companies including Starbucks, Amazon, and McDonalds also having had their tax policies reviewed by the Commission. Apple has also listed the investigation as a risk factor to investors in its financial statements for 2015, noting that if the tax rates were to change, Apple’s “financial condition, operating results and cash flows could be adversely affected.” A ruling on the matter could come as early as March.