The U.S. government will limit a process that allowed people to sign up for health insurance under Obamacare outside of the normal enrollment period, after health insurers complained that the special sign-up windows were letting people into the program only when they got sick.

Typically, individuals have from about November to January to buy coverage under the Affordable Care Act. In some cases, though, they’re allowed to sign up outside that period, such as when they have a child. The government closed down sign-ups for six limited circumstances, including for people who were already eligible or enrolled in coverage after leaving a job, a program known as COBRA.

The government is also tightening an exception that let people sign-up when they moved, by clarifying that people can’t get coverage based on a short-term or temporary relocation, the Centers for Medicare and Medicaid Services said in a blog post on Tuesday. It also plans to more tightly enforce other limits on enrollment by making sure people are qualified to sign-up in the remaining special circumstances.

After using the special enrollment periods as a way to get more people signed up for Obamacare, the U.S. is now moving to address insurers concerns about the program. Companies including UnitedHealth Group Inc. have said they may exit Obamacare’s marketplaces because they’re struggling to turn a profit. UnitedHealth has pointed to individuals who sign up outside the regular enrollment periods as being more costly to insure.

“While this is an important first step, more needs to be done to validate special enrollment requests,” said Clare Krusing, a spokeswoman for the lobby group America’s Health Insurance Plans. “It’s critical that there is a process in place to avoid potential abuse of special enrollment periods and to ensure a stable, affordable market for consumers.”

The Affordable Care Act created limited windows for people to enroll, as an incentive to sign up for both the sick, who need coverage right away, and the healthy, who may need it in the future. The U.S. has already said it’s eliminating the tax-time special enrollment period, during which people who were facing tax penalties for going uninsured were eligible to buy coverage.