CHICAGO (CBS) — A Pennsylvania company that manages the power grid for Illinois and a dozen other states was asking consumers to cut back on their electricity use Tuesday.

WBBM Newsradio’s Regine Schlesinger reports, as frigid conditions tighten their grip on Chicago and much of the rest of the country, PJM Interconnection – which operates the transmission grid for ComEd and many other power companies – said people are cranking up electric heaters and thermostats.

That puts a strain on power plants, especially those that must buy coal and natural gas at higher rates to keep their turbines spinning. Dotter said PJM already broke two records this month for power use, and demand could break another record on Tuesday.

“We’re watching the power supplies very closely. Supplies are expected to be tight,” spokesman Ray Dotter said.

PJM was asking people to cut back on power consumption to ease the strain on electric grids.

“Don’t turn on things you don’t need. Don’t be unsafe. Don’t be unhealthy. If you can turn back the thermostat a little bit, that would certainly help,” Dotter said.

PJM also recommended people avoid using electric appliances from 6 a.m. to 10 a.m. and 5 p.m. and 9 p.m., when power use is at its highest.

It’s asking customers to use major appliances such as stoves, dishwashers, and clothes dryers during midday, or after 9 p.m.