The administration is warning hundreds of thousands of consumers they risk losing taxpayer-subsidized health insurance unless they act quickly to resolve issues about their citizenship and immigration status.
Officials told The Associated Press on Tuesday that letters are being sent to about 310,000 people, many of whom haven't responded to previous outreach.
Those consumers need to upload their documents by September 5 to HealthCare.gov, or mail them in.
Otherwise, their coverage will end on Sept. 30.
The letters are being sent in English and Spanish.
About 8 million people signed up for subsidized private coverage under President Barack Obama's law, but at one point more than 2 million had discrepancies that could have affected their eligibility. Officials say that's been greatly reduced.