HARRISBURG -- Deregulation of electric rates in 2010 in many areas of the state could constitute "the biggest tax increase in Pennsylvania history," state Senate Democrats said yesterday.

Since 1996, the rate at which many Pennsylvania energy companies have been able to recoup power plant construction costs from consumers has been capped.

But by 2010, the rate caps will expire for customers in parts of western Pennsylvania served by West Penn Power, plus many residential and business customers in northeast and central Pennsylvania, along with the Lehigh Valley and Philadelphia areas. Rate caps for Duquesne Light already have ended.

"Nobody is going out of business'' in the state's electricity industry, said Sen. Vincent Fumo, D-Philadelphia, noting high profit margins and well-salaried executive of electric utilities. "[Allowing these caps to expire] would be the biggest tax increase in the history of the Commonwealth since Ben Franklin."

He was joined in his criticism by Democratic Sens. Jim Ferlo of Highland Park, Wayne Fontana of Brookline and Sean Logan of Monroeville.

"Utility shutoffs have already risen 37 percent compared to last year,'' said Mr. Logan. "Unless we take decisive steps soon, I fear for how many people will be unable to pay and will have their electricity shut off when deregulation hits its statewide peak in 2010.''

The Democrats held a Capitol news conference announcing plans for a series of bills to limit or defer rate increases. One bill would limit annual electric rate increases to the lesser of 5 percent or the yearly rate of inflation (as measured by the Consumer Price Index).

Another option would be to extend the rate caps for 10 more years, Mr. Fumo said.

He acknowledged that rate-cap bills would have to wait for action until the fall. Mr. Fumo is retiring from the Senate on Nov. 30, but the other Democrats vowed to fight on.

Utility officials didn't like the Democrats' criticism.

"There's no way to avoid paying these [ongoing power generation] costs," Douglas L. Biden, the president of Electric Power Generation Association, said. "This [Democratic plan] is not a legal option, and these utilities would go to court" to fight it.

Mr. Fumo and Sen. Lisa Boscola, D-Lehigh, reviewed potential increased monthly electricity bills for their residents if the caps were to expire.

West Penn/Nittany Power customers could see their bills spike more than 60 percent, they said, according to projections from state Consumer Advocate Irwin "Sonny" Popowski.

Other rate spikes would affect customers of PPL Electric Utilities in central and eastern Pennsylvania, PECO in Philadelphia and FirstEnergy.

Mr. Biden contended that high rate increases don't reflect utility companies specifically but rather their holding company's profits. Numbers used by Senate Democrats are also misleadingly selective, only including the most profitable companies .

Concerning opposition from the electric industry and its lobbyists, Mr. Ferlo said: "Let's get ready to rumble."