CHICAGO, July 30 — Tens of thousands of people here have signed petitions protesting a permit granted in Indiana that allows the largest oil refinery in the Midwest to discharge more pollutants into Lake Michigan.

The petitions, which advocates say they expect to deliver next week to Gov. Mitch Daniels of Indiana, reflect growing concerns in the Great Lakes States that the permit undercuts efforts to clean up Lake Michigan.

Organizers said Monday that they had collected 45,000 signatures.

“At a time when we’ve spent billions and billions of dollars investing in the rehabilitation of the Great Lakes, we should not be taking a step backward,” said Cameron Davis, the president of the Alliance for the Great Lakes, a conservation advocacy group that has participated in the petition drive.

Last week, by a vote of 387 to 26, the United States House of Representatives approved a resolution urging Indiana to reconsider the permit. The resolution was introduced by Representatives Rahm Emanuel, Democrat of Illinois, and Vernon J. Ehlers, Republican of Michigan.