Idaho Falls, Idaho (AP) — Federal regulators are now investigating a power outage in eastern Idaho that left 70,000 people without electricity for up to 10 hours amid a subzero cold snap.

The Post Register reported Friday the Federal Energy Regulatory Commission is reviewing the outage, which came after Rocky Mountain Power, a subsidiary of PacifiCorp, made repairs to a substation.

As part of FERC's probe, regulators are collecting data about the reliability of Rocky Mountain Power's system to discern whether rules violations helped exacerbate the outage. Fines are possible.

Meanwhile, Rocky Mountain Power officials say the substation maintenance, recommended by equipment manufacturers, was planned for "a little late in the year, but was seen as critical." Some local utilities that were affected including in Idaho Falls say they wished they'd had more warning.