Amgen Inc. is grappling with over $10 billion in back taxes claimed by the IRS, leading to substantial Notices of Deficiency for multiple tax years. The company's failure to disclose its tax liabilities has prompted a class action lawsuit from investors who purchased shares during the implicated period, highlighting severe financial repercussions for both the firm and its stakeholders. As Amgen grapples with these challenges, its stock price has taken a hit, resulting in significant losses for its investors.