The Obama administration has sent incorrect tax information to 800,000 customers of Healthcare.gov, the federally run insurance exchange, and is asking those people to wait to file their taxes until they get corrected information.

The error shows up on a 1095-A form that’s mailed to those receiving subsidies under the Affordable Care Act and is a result of 2015 premiums being used in a calculation instead of those from 2014. Officials said the error will result in some paying more taxes and others paying less.

“It’s just another black mark on the administration’s handling of the health care act,” Roberton Williams, a senior fellow at the nonpartisan Tax Policy Center in Washington, told the Associated Press. “They were hoping for a clean season.”

Andrew M. Slavitt, the deputy administrator at the federal Centers for Medicare and Medicaid Services, said officials did not know why the mistake had occurred, according to The New York Times.

About 50,000 of those who received the erroneous forms are estimated to have already filed their 2014 taxes. Taxpayers can sign onto their accounts at Healthcare.gov or call 800-318-2596 to find out if they’re among those who got incorrect forms.

This isn’t the first instance of tax forms being incorrect because of the healthcare law. About 100,000 Californians have received similarly erroneous tax forms from Covered California, that state’s healthcare exchange.

The Obama administration also announced that there would be a special enrollment period for those taxpayers who were unaware of the penalty for not having health coverage or an exemption from carrying it. The period will run from March 15 to April 30. Some of the state exchanges are also extending their enrollment periods.

-Steve Straehley

To Learn More:

New Woes for Healthcare.gov: Wrong Tax Info Sent Out (by Ricardo Alonso-Zaldivar, Associated Press)

Tax Error in Health Act Has Impact on 800,000 (by Robert Pear, New York Times)

Feds Sent Incorrect Tax Information to 800,000 People on ObamaCare (by Peter Sullivan and Sarah Ferris, The Hill)

Is your Form 1095-A correct? (Healthcare.gov)

Covered California Sends Wrong Tax Info to 100,000 Customers (by Ken Broder, AllGov California)