TORONTO -- Ontario NDP Leader Andrea Horwath says the provincial government ordered hydro distribution companies to place partisan messages on customers' bills that advertise the Liberals' plan to cut electricity rates.

Horwath says the order, signed by Energy Minister Glenn Thibeault and deputy premier Deb Matthews, said the messages promoting the government's Fair Hydro Plan were to appear on bills from July 2017 to July 2018, a period which ends a month after the next provincial election.

Horwath says the order to the companies dictated the precise wording of the messages.

Earlier this year a distribution company in Niagara-on-the-Lake, Ont., complained that the government was politicizing utility bills with the order.

The Liberal government announced a plan to cut hydro rates by 25 per cent last spring following months of public outcry over rising bills.

Thibeault says the messaging was meant to help ratepayers understand their bills.