BP faces a new battle, this time over its existing air emission limits.

The charge comes from Illinois officials and environmental groups that Indiana regulators let the company bypass federal pollution rules. It's the second petition in the last month filed with the Indiana Office of Environmental Adjudication regarding decisions made about BP's Whiting plant.

It's unclear whether the petition, filed against the Indiana Department of Environmental Management, could delay a new upcoming BP air permit necessary for the refinery's multibillion dollar expansion plans.

The Illinois-based petitioners say BP didn't adequately prove it deserved an exception, granted by IDEM, to its air emissions limits of particulate matter, or small particles and liquid composed of chemicals, metals and dust.

BP requested the variance to the refinery's existing air permit after the U.S. Environmental Protection Agency made a change calling for a 50-percent reduction in particulate matter emissions.

In its request for the variance, BP said complying with the adjusted limits would "impose an extreme hardship on BP" because compliance "is neither technically nor economically feasible."

The petitioners say BP did not provide evidence of technical or economic infeasibility and that IDEM did not compel BP to do so.

IDEM Commissioner Tom Easterly issued the yearlong variance July 5, which became effective July 23.

In his decision approving the variance, Easterly wrote: "IDEM has determined that the requested limits ... will not result in environmental harm to air quality in Lake County."

But the petitioners say air quality is at stake in more than just Lake County.

Particulate matter emissions, known to cause or exacerbate respiratory conditions, can travel by air for many miles, the petition states. As such, "On some days, emissions from the Whiting Refinery blow into Illinois and the City of Chicago," the petition states.