The most contentious aspect of the Patient Protection and Affordable Care Act (ACA) is the individual mandate requiring that most documented U.S. residents obtain health insurance or pay a tax penalty. Many experts have long advocated a mandate as a central pillar of private-sector–based health care reform. Others, however, have argued that a mandate is not necessary for successful reform.
Chandra, Amitabh, Jonathan Gruber, and Robin McKnight. "The Importance of the Individual Mandate — Evidence from Massachusetts." Health Policy and Reform. January 12, 2011.