(AP) — Those huge list prices charged by hospitals are getting attention, but a federal law that limits what financially vulnerable patients can be billed seems to have shifted to the back burner.

A provision in President Barack Obama’s health care overhaul says most hospitals have to charge uninsured patients no more than what people with health insurance are billed.

But consumer groups that lobbied to get the provision are disappointed.

The law applies only to nonprofit institutions — about 40 percent of hospitals are exempted.

There isn’t a clear formula to determine which patients qualify for help, and the Internal Revenue Service has yet to issue final rules explaining how the provision would work.

The administration says it expects hospitals to comply, but it can’t say how many are doing so.