The NDP says one reason hydro bills are rising is that utilities are being allowed higher profits. (CBC)

The New Democrats say they've uncovered yet another reason electricity bills are going through the roof — a big hike in the guaranteed profits for Ontario electricity utilities.

The Ontario Energy Board has determined that the return on equity — the regulated rate of return — for power distributors and transmitters should jump to 9.85 per cent from 8.39 per cent.

NDP Leader Andrea Horwath says the change means an additional $240 million a year in guaranteed profits for utilities, and higher rates for consumers.

Horwath says families will be forced "to fork over another $60 a year to fatten the profits of already profitable utilities."

Premier Dalton McGuinty ducked all questions about the guaranteed profits, but said electricity rates must go up to pay for modernizing an outdated and dilapidated system.

The Progressive Conservatives, meanwhile, say another energy agency, the Ontario Power Authority, has increased its bureaucracy by over 450 per cent, adding even more to hydro bills.

Opposition Leader Tim Hudak says despite its swelling bureaucracy, the OPA still spent $80 million on outside consultants — but hasn't come up with a promised long-range energy plan for Ontario.