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

Horwath said the order, signed by Energy Minister Glenn Thibeault and deputy premier Deb Matthews on June 15, instructed companies that 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.

The order dictated the precise wording of the messages and is a "heavy-handed" way to advertise a Liberal plan on the cheap, she said.

"It's a desperate attempt by this government to reach Ontarians and try to show themselves in a better light," said Horwath.

The messages should inform customers that the government's hydro plan "substantially lowers electricity bills for typical residential customers," says the order, obtained by the New Democrats. They should also include an insert that has the Ontario government trillium logo in a "reasonably prominent place" along with the words "Ontario's Fair Hydro Plan" and "Bringing electricity bills down".

The order goes on to state that the companies must include information about the 25 per cent cut, spell out that rate increases will be held to the rate of inflation for four years and that the cut will also help small businesses and farms.

"It's not fair to the people of Ontario that this Liberal government decides they're going to use utility bills to make some partisan gains," Horwath said. "It's just totally inappropriate."

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.

"It's (about) trying to make sure people understand clearly what their bills are all about," he said. "Sometimes we treat people like they're energy experts rather than just trying to understand their bill."

Earlier this year a distribution company in Niagara-on-the-Lake, Ont., complained that the government was politicizing utility bills with the order. The company also said calling the rate reduction "savings" is also questionable when much of it will have to be repaid in the future.

"Nobody likes to receive a bill but we owe it to our customers to make them as understandable and honest as possible," Jim Ryan, chair of Niagara-on-the-Lake Hydro, said in a statement. "Putting political messages on the invoice is simply wrong."