Facebook is being sued by the Internal Revenue Service, which says the social networking giant owes the US government more than $9 billion in unpaid taxes related to its decision to shift profits to its Irish subsidiary, Reuters reported Tuesday.

The lawsuit, which went to trial on Tuesday in a San Francisco court, alleges that Facebook understated the value of intellectual property it sold to its Irish subsidiary in 2010, the news agency reports.

Facebook hardware chief Andrew Bosworth and Chief Technology Officer Mike Schroepfer are expected to testify in the trial, expected to last three to four weeks.