KELLI KENNEDY, Associated Press

FORT LAUDERDALE, Fla. (AP) — A new report warns that insurance companies — perhaps more than initially thought — may be charging the sickest patients extra for drugs under the federal health law to discourage them from choosing certain plans.

One of the cornerstones of President Barack Obama’s signature health law forbids insurance companies from turning away people with pre-existing conditions such as diabetes or cancer. But advocacy groups say insurance companies are still discriminating against them by putting their medications in a high-priced option.

The customer is then required to pay a percentage of the drug, which costs far more than a flat co-pay.

A study published Wednesday in the New England Journal of Medicine only examined HIV drugs, but noted the problem applies to mental illness, rheumatoid arthritis and other chronic conditions.