One-fourth of health plans sold on health insurance exchanges created through the Affordable Health Act appear to offer unequal benefits for mental and physical illness, a new study concludes. A federal “parity” law requires equal benefits for general medical and mental health care.

The study, by researchers at the Johns Hopkins Bloomberg School of Public Health, found some of the health plans that appeared to offer unequal mental health benefits had financial disparities such as different co-pays or deductibles for mental and physical health services, USA Today reports. Many had stricter requirements for prior authorizations from insurers before patients can receive mental health services. Prior authorizations compel a patient to obtain approval for a medical visit or service before being seen by a doctor in order for that visit to be covered, the researchers note in a news release. This can add lengthy delays to the process of obtaining treatment, said lead author Colleen Barry.

“Our concern was that health plans may have an incentive to avoid enrolling individuals who use mental health services because their care tends to be more costly on average,” Barry said. “This would go against the philosophy of parity, which was to level the playing field. Our study suggests that some plans may still be offering people with mental illness insurance benefits that are less generous than benefits for other medical conditions.”

Under the Affordable Care Act, all new small group and individual market health plans must offer mental health services, and cover them on par with medical benefits, the article notes. For example, if the plan has a 10-visit limit for psychiatric visits, it must also have the same limit for primary care physician visits.

The study looked at benefit brochures offered during the first Affordable Care Act enrollment in two state-run exchanges. The research appears in the journal Psychiatric Services.