Microsoft said on Wednesday the U.S. Internal Revenue Service (IRS) in September notified the company that it is seeking an additional tax payment of $28.9 billion, plus penalties and interest, for tax years from 2004 to 2013. Microsoft disputes the figure. The Redmond, Washington-based company is involved in a long IRS audit focusing on how companies allocate their profit among different countries and jurisdictions. This is a mechanism that critics say allows corporations to minimize their tax burden.

For over a decade, Microsoft has been fighting the audit, which the government has described as an examination of transfer pricing. In a legal filing, Microsoft said it would contest the proposed adjustments in an appeals process within the IRS that can take several years. It added that Microsoft also plans to contest any unresolved issues through judicial proceedings.

The audit examines intercompany deals that Microsoft struck over the years, including one in which it transferred some of its software development rights to a subsidiary in Puerto Rico for less than market value. For this part of the dispute, the IRS has sought a series of summonses to Microsoft for documents and testimony from its current and former executives.

When it first received the summonses, Microsoft set out to quash them. It argued that the IRS had broken federal rules by hiring Quinn Emanuel to question witnesses in the case and by allowing the firm’s attorneys to act as the lead attorneys. The lawyers were “focused on winning,” a Microsoft attorney told the court, and that was not the IRS’ mission.

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But the summonses were granted, and the dispute grew more contentious as Hoory began questioning current and former executives about their dealings with the IRS. The company argued that the questions were broad and could be used to build a case against the executives for evading taxes. Ultimately, the IRS convicted several executives and fined them millions of dollars.

In its filing on Wednesday, Microsoft said it disagreed with the proposed adjustments and will continue to fight them in an appeals process within the IRS, which can take several years to complete. It also argues that the figures do not consider taxes paid by Microsoft under the Tax Cuts and Jobs Act, which could reduce the final bill by up to $10 billion.

It is not unusual for the IRS to share its initial findings in a tax dispute with companies under audit. Still, Microsoft said it would continue to fight the determinations and consider taking the matter to court. The dispute will impact the software giant’s financial results for several years. In its filing, Microsoft said it expects to record a charge of up to $5 billion related to the case in the quarter ending December. That charge is based on the latest estimate of the tax liability associated with the audit and other factors.