According to the US Internal Revenue Service (IRS), Microsoft owes $28.9 billion to the US Treasury in unpaid taxes, as well as penalties and interest. The figure, which Microsoft rejects, is based on a lengthy IRS investigation into how Microsoft distributed profits across countries and jurisdictions between 2004 and 2013.

Critics of the practice, known as transfer pricing, say companies often use it to minimize their tax burden by reporting lower profits in high-tax countries and higher profits in lower-tax jurisdictions.

Microsoft, headquartered in Redmond, Washington, said it complied with IRS rules and would appeal the agency’s decision. This process is expected to take several years.

The company said it has since changed its practices, so “the issues raised by the IRS relate to the past but not to our current practices.” Microsoft believes that according to the tax legislation enacted by Donald Trump, up to $10 billion will be cut from all taxes after the audit. Microsoft shares fell $1.42 to $331.