Federal health officials are cracking down on consumers’ ability to buy health plans through HealthCare.gov outside formal enrollment seasons, responding to complaints from insurers that some people have waited to get coverage until they were sick.

Under rules announced Wednesday by the Department of Health and Human Services, people who want coverage under five main reasons for a “special enrollment period” will need to supply documents proving that they deserve an exception from the regular sign-up times.

The new requirement will be for people in the 38 states that rely on the federal insurance exchange who need to begin or change coverage because they have moved, had a baby, adopted a child, gotten married or lost other health coverage. Until now, people have been able to sign up outside regular enrollment periods for these reasons, plus others, simply by checking a box.

The Affordable Care Act, the law that created the insurance marketplaces, allows for consumers to get health plans throughout the year under limited circumstances. The question of how easy it should be to do so has emerged as a tug of war between consumer advocates, who argue for flexibility, and the insurance industry, which contends that some people are abusing the system by avoiding coverage until they need medical care.

Under the ACA, the federal HealthCare.gov website and separate marketplaces run by some states offer health plans for people who cannot get affordable coverage through an employer. By restricting when most people can enroll – the most recent period ran from November through January – the idea is to make it difficult for consumers to buy insurance only when they need care, behavior that raises insurers’ costs and the prices they charge.

But many consumers have used special enrollments. According to federal figures, more than 1 million people last year bought health plans by using one of the five special reasons that will now require documentation. Nearly 150,000 more got coverage during a one-time window for people who otherwise would have faced penalties for being uninsured.

America’s Health Insurance Plans and the Blue Cross Blue Shield Association have urged federal health officials to require documentation, and both groups praised the new rules Wednesday.

The groups had commissioned a joint consultant’s study, which found that people enrolling outside the usual time had much higher medical claims than other customers with ACA coverage.

On the other hand, Judy Solomon, vice president for health policy at the Centers for Budget and Policy Priorities, said requiring documents is burdensome and unnecessary because there is no real evidence that consumers are lying to get special enrollments.

She noted that, during HealthCare.gov’s first two years, some consumers were improperly denied coverage because the system had trouble handling other kinds of documentation, such as proof of immigration status, to verify eligibility.

Last month, federal health officials announced a related change, eliminating some categories that had qualified for special enrollments, such as moves that were temporary.