Under federal rules, anyone who receives an insurance subsidy must file a tax return to verify that the person was eligible and received the proper amount of financial assistance based on household income.

When the federal insurance marketplace opens for the third enrollment season next Sunday, users will see a new question: “Did your household file a 2014 tax return and reconcile any premium tax credit you used?”

If the answer to that question is no, consumers risk losing the subsidies they receive to help pay premiums. Without such assistance, many would find insurance unaffordable.

Many of the people potentially affected have incomes so low that they would not otherwise have to file tax returns. But if they received insurance subsidies in 2014, they were required to file this year.