Federal energy regulators plan to impose new security rules on electric utilities to make sure they protect major substations and other facilities critical to the operation of the electric grid.

The Federal Energy Regulatory Commission said it would require physical protection for locations which, if badly damaged, could produce cascading blackouts or other widespread problems, reports The Wall Street Journal.

FERC directed a standards-writing organization called the North American Electric Reliability Corp. to work with utilities to determine which sites are essential, define threats and develop physical-protection standards, reports The Wall Street Journal. The standards should be based on "objective analysis, technical expertise and experienced judgment," the agency said.

The standards-drafting group must submit a proposal in 90 days. Under the system established by Congress, FERC lacks authority to rewrite proposals; it must accept or reject them or ask the group to revise them, says The Wall Street Journal.

The agency provided no detailed guidance on what it wants from the standards-writing group, which is dominated by utilities which would face fines of up to $1 million a day for each infraction of new rules.

In a statement, FERC's acting chairman, Cheryl LaFleur, said the agency was persuaded to act "because the grid is so critical to all aspects of our society and economy."