DENVER (AP) — Colorado took the unusual step of inviting the U.S. Environmental Protection Agency to downgrade the air quality rating of the state's biggest population center, and not everyone thinks that was a good idea.

The EPA held a hearing Friday on whether to lower the ozone status of Denver and eight other northern Colorado counties from "moderate" to "serious." That would force the state to work harder to reduce harmful pollution but also bring tougher and costly regulations for businesses.

The agency expects to decide by the end of the year.

The EPA acted after Democratic Gov. Jared P...