The Progressive Conservatives at Queen’s Park are asking Ontario’s budget watchdog to conduct a full costing of the Liberal government’s plan to lower hydro bills.

Premier Kathleen Wynne announced last week a 17 percent reduction in hydro bills for this summer as contracts with energy providers are extended over a longer period of time.

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

The Premier also said in question period on Thursday that 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 and have sent a letter to the financial accountability officer, asking him to investigate.

Wynne’s $25-billion figure does not appear in the hydro relief announcement’s background documents, which say the plan will involve “annual interest costs not exceeding $1.4 billion.”