(Bloomberg) — As many as 6 million taxpayers will have to pay a penalty of as much as 1 percent of income because they went without health insurance in part or all of 2014, the Treasury Department said.

The penalty, part of the Patient Protection and Affordable Care Act, is designed to encourage people to sign up for health insurance using the expanded options and financial assistance available under the law. The penalty would apply to about 2 percent to 4 percent of all taxpayers for 2014.

Tax filing for 2014 opened Jan. 20, and the Internal Revenue Service's Form 1040 — for federal income tax — includes a new Line 61 asking if the taxpayer has health insurance. Three-quarters of taxpayers won't have to do anything more than check that box, said Mark Mazur, the department's assistant secretary for tax policy. The remainder will have to to take additional steps, though most won't pay a penalty, he said on a conference call with reporters.