TOLEDO, OH (AP) – Federal regulators are proposing a $40 million fine against the builder of a multistate natural gas pipeline.

The Federal Energy Regulatory Commission says the pipeline company used diesel fuel and other toxic substances while drilling under a river in Ohio four years ago.

The proposed fine stems from an accidental spill of 2 million gallons in 2017. It’s the second hefty penalty sought against Dallas-based Energy Transfer Partners and its subsidiary Rover Pipeline within the past year.

The company says it didn’t have any knowledge or involvement in using the diesel fuel. It says a subcontractor’s rogue employee is to blame.