CNBC: “Microsoft received Notices of Proposed Adjustment from the Internal Revenue Service for an additional tax payment of $28.9 billion, the company said in an 8-K filing Wednesday. Microsoft said the dispute concerns the company’s allocated profits between countries and jurisdictions between 2004 and 2013. It said up to $10 billion in taxes that the company has already paid are not reflected in the proposed adjustments made by the IRS. Microsoft plans to contest the notices through the IRS’ administrative appeal and is willing to go to judicial proceedings, if necessary.”
See also the related SEC Filing.