(Reuters) - A Michigan regulator said this week it is seeking public comment on a proposed permit that would allow Marathon Petroleum to boost crude throughput at its Detroit refinery.

Marathon filed an application with the state in March to run its 140,000 barrel per day refinery continuously at full capacity by removing monthly and annual throughput limits. The plan is opposed by local environmental groups because increasing throughput increases refinery pollution.

The refinery's current permit caps the facility's capacity at 140,000 barrels per day (bpd) on an annual average.

Marathon currently relies on periods of shutdown or reduced production to meet the annual average limit, a spokesperson for the Michigan Department of Environment, Great Lakes, and Energy said.

Marathon declined to comment on whether it plans to boost throughput beyond 140,000 bpd.

The Detroit refinery emits less pollutants than its current permit allows, according to Marathon and regulators.

The facility is located in Wayne County, Michigan, an area with significant industry presence that is out of compliance with national standards for sulfur dioxide emissions.

To offset pollution increases, Marathon has proposed several projects including upgrading process heaters to phase out the crude flare.

Marathon has violated air quality rules and regulations in the past, but that cannot prevent Marathon from seeking this permit, regulators said.

The company lost an appeal in 2022 to be exempt from a rule requiring it to enclose petroleum coke at the Detroit refinery in order to prevent dust from being released.

A public hearing on the proposed permit is scheduled for May 22.

(Reporting by Laura Sanicola; Editing by Liz Hampton and Chris Reese)

By Laura Sanicola and Nicole Jao