The Internal Revenue Service (IRS) has notified tech giant Microsoft that it owes a substantial $28.9 billion in back taxes, alongside penalties and interest, for the tax years spanning 2004 through 2013. This information comes to light via an official filing with the Securities and Exchange Commission (SEC).

Microsoft’s Corporate Vice President for Worldwide Tax and Customs, Daniel Goff, responded to the audit findings in a blog post. Goff maintained that the company had undergone significant changes in its corporate structure and practices since the period covered by the audit. He emphasized that the IRS’s concerns were pertinent to the past and not indicative of Microsoft’s current practices.

One key point of contention raised by Goff is that the IRS’s proposed adjustments fail to account for the amounts Microsoft paid under the Tax Cuts and Jobs Act. He suggests that this omission could potentially reduce the final tax liability by as much as $10 billion. Furthermore, Microsoft asserts that the IRS has disputed the company’s approach to allocating profits internationally through a method known as cost-sharing.

Microsoft is taking a firm stance in response to the IRS’s proposed adjustments, indicating that it intends to “vigorously contest” them. The company also stated in its blog post that it does not foresee a quick resolution to this dispute, with expectations that it may linger for at least the next 12 months.

Separately, Microsoft recently secured a legal victory over the Federal Trade Commission (FTC), which had attempted to prevent the tech giant’s acquisition of Activision Blizzard for a whopping $68.7 billion. This acquisition deal is set to be finalized on October 13th, according to the company’s announcement.