Because of paperwork problems, more than 300,000 individuals risk losing some or all of their health-insurance subsidies under the Affordable Care Act, Obama administration officials announced last month.

Those individuals faced a Sept. 30 deadline to submit information such as tax returns, wage statements or letters from employers to verify income.

Enrollees who don’t get those paperwork issues taken care of, or those who miscalculated their estimated 2014 income could face an unwelcome surprise during 2015 tax season, when they could be asked by the government to pay back subsidies they didn’t qualify for, according to a recent Wall Street Journal article.

Individuals who enrolled for coverage in the ACA marketplace in 2014 may not be aware that they have been receiving advance tax credits toward their health insurance premiums. The subsidies were based on estimated 2014 income.

When they file their income taxes in 2015, they will have to reconcile those credits based on their actual 2014 income, which could be higher than what they estimated–and some may end up having to pay the government back.

“They are going to be surprised and need to know what just happened, and a lot of people will be frustrated,” said Mark Ciaramitaro, vice president, health-care services H&R Block, in an interview with the Wall Street Journal.

Additionally, another 115,000 people who enrolled in plans through were deemed at risk for losing coverage if they didn’t provide requested documents supporting their citizenship or immigration status by Sept. 5.