UnitedHealth Group faces an IRS investigation into its foreign subsidiary tax practices. The probe focuses on transfer pricing from 2017 through 2020.

The IRS seeks to significantly increase the company's taxable income for that four-year period. These adjustments could also impact taxable income for subsequent years.

UnitedHealth received formal notices from the agency in March. The company plans to vigorously contest the proposed adjustments and maintains its tax positions are properly supported.

The investigation tempers investor sentiment following a strong second-quarter earnings report in July. UnitedHealth beat analyst expectations and raised its full-year financial guidance during that period.