Almost six million Americans will face a tax penalty under the Affordable Care Act for not obtaining health insurance, according to an estimate from the Congressional Budget Office (CBO).

Most of those who will face the penalty will be middle-income workers, the Associated Press reports. The estimate is significantly larger than the CBO’s previous estimate of four million people, which was calculated in 2010. Most of the increase in the estimate is due to changes in the office’s projections about the economy, and to the effects of new federal legislation, the article notes.

Beginning in 2014, almost all legal residents of the United States will have to carry health insurance or face a tax penalty. Exemptions will be made in cases of financial hardship and religious objections. The penalty is expected to be about $1,200 per person in 2016, the first year the penalty will fully be in effect.

According to a spokeswoman for the Health and Human Services Department, 98 percent of Americans will not be affected by the penalty.