Ontario's budget watchdog is planning a report examining the Liberal government's plan to lower hydro bills.

Progressive Conservative Leader Patrick Brown has written to the financial accountability office, asking them to investigate the plan with a full costing analysis.

A spokeswoman for the office says they'll take Brown's letter under consideration, but they had already been planning to examine the hydro plan.

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The recently announced 17-per-cent reduction in hydro bills comes this summer thanks to a move the Liberals say is like refinancing a mortgage over a longer period of time.

Premier Kathleen Wynne has acknowledged it will cost ratepayers more in the long run, but she says savings are needed now because people are struggling.

She has said the extra interest costs related to the plan would amount to $25 billion over 30 years, but the Tories say they're not clear on how the Liberals arrived at that number.