In 2016, nearly six million U.S. residents are expected to pay a tax penalty under the Affordable Care Act for not purchasing health insurance, two million more individuals than estimated in April 2010, according to a report released by the Congressional Budget Office.

CBO said about 85 percent of the increase could be attributed to changes in projections for the economy and the effects of the ACA since it was enacted. CBO said the Supreme Court’s decision to allow states to opt out of the Medicaid expansion accounts for the remaining 15 percent, because some states will forgo the expansion, increasing the number of uninsured residents.

A total of about 30 million non-elderly individuals are expected to be uninsured in 2016 and one-fifth of those will pay the penalty. However, between 18 million and 19 million residents will be exempt from the penalty. For example, undocumented immigrants, American Indians and low-income individuals do not have to pay the penalty. The remaining uninsured residents will not have to pay the penalty because of a hardship or their religious beliefs.