The rules would have required the refinery to halve the amount of microscopic pollution the refinery emits. However, Indiana regulators sided with BP's contention that the change would not be technically or economically feasible.
Last week, attorneys for two environmental groups, the city of Chicago and the state of Illinois asked an Indiana judge to overturn the Indiana decision, saying BP hasn't shown why the problem couldn't be resolved through engineering.
It's the second dispute to swirl around the site in a month. BP late this summer abandoned plans to release more ammonia and suspended solids into Lake Michigan in order to allow more refining of Canadian oil. That decision was precipitated by a storm of criticism, primarily from Illinois.