CHICAGO | ComEd customers in Illinois will soon see an overall 6 percent increase in their electric bills after the Illinois Commerce Commission approved a delivery rate increase for the utility giant Wednesday.

Consumer advocacy groups vowed to appeal the decision after the ICC approved ComEd's rate increase request for the second time in as many years. The $270 million in revenue for ComEd will add $4.50 to the average consumer's bill of about $81.

ComEd originally requested a $360 million increase last October to reflect higher costs of materials used to maintain and upgrade infrastructure, including power wires and utility poles, said ComEd spokeswoman Alicia Zatkowski.

In late 2006, the ICC granted ComEd a delivery rate increase of $83 million, then about 5 percent overall. The delivery rate makes up about 30 percent of the average residential user's bill.

Meanwhile, the cost of the energy portion of the bill has mounted ever since a freeze on rates ended in 2006 and prices became dependent on an auction process.

Altogether, consumers have seen a 20 percent increase in utility bills since the end of the freeze, according to AARP.

That's hurtful to seniors who live on fixed incomes, said Bob Gallo, AARP Illinois' state director.

"With cold weather coming, individuals are looking at turning down their thermostats so they can pay for their prescription drugs," he said.

ComEd is inflating its costs and doesn't deserve the rate increase, said Citizens Utility Board spokesman Jim Chilsen.

"We are all for ComEd remaining healthy and keeping the lights on. The company did not need such a large rate hike in order to do its job," he said. "It's rolling in near-record profits."

ComEd is a subsidiary of Chicago-based Exelon Corp. and provides electricity for 3.8 million customers across northern Illinois.

St. Louis-based Ameren Corp., which provides electricity and gas to more than 2 million customers in the state, also seeks $207 million in rate increases from the ICC.