WASHINGTON — Some 310,000 people with inconsistencies in their citizenship and immigration materials might lose their federal marketplace health coverage Sept. 30 unless they provide proper supporting documents by Sept. 5, the Obama administration announced Tuesday.

In May, the Department of Health and Human Services began contacting about 2 million people about discrepancies or errors in the personal information they’d provided in their insurance applications.

The problems stem, in part, from an administration policy that allowed applicants to self-report information about their incomes, citizenship and household size, all of which contribute to determining their eligibility for tax credits to help pay for coverage.

The self-reporting system was adopted because the federal marketplace technology to verify all applicant information wasn’t fully functional. For the first year of operation, the federal exchange used a scientific sampling process to weed out applications that understated household income.

About 970,000 people had information about their citizenship or immigration status on their applications that didn’t match data in government records.

The department has resolved the inconsistencies for about 450,000 people and is working on another 210,000. On Tuesday, HHS sent letters to roughly 310,000 others with citizenship or immigration matching errors who haven’t yet responded to previous attempts to resolve the matters.

The final notices, in English and Spanish, remind recipients they must provide proper documents by Sept. 5 or risk losing their coverage at the end of next month.

These people will also receive two phone calls and an email seeking to remind them before the deadline. Those whose information is currently being processed or has already been verified won’t receive letters.

“We want as many consumers as possible to remain enrolled in marketplace coverage, so we are giving these individuals a last chance to submit their documents before their coverage through the marketplace will end,” said Marilyn Tavenner, the administrator of the Centers for Medicare & Medicaid Services at HHS.

The notices provide instructions for submitting the necessary information and how to keep coverage intact.

“Since this is an urgent matter, we are activating our networks on the ground to reach people directly in the communities where they live,” Tavenner said. “Whether it is online, via our call center or with one of our local partners, consumers will have a number of ways to find the help they need to continue their coverage.”

Community organizations and other groups will assist with outreach efforts.

People with outstanding income-verification issues will “hear from the marketplace at a later date,” according to an HHS press statement.

States that operate their own marketplaces are working independently to resolve any similar problems.