TORONTO - Ontario's New Democrats turned up the temperature on rising home electricity costs Monday by challenging the governing Liberals to zap the provincial portion of the HST off hydro bills.

Consumers across the province are struggling to pay sky-high electricity costs and simply can't afford an extra eight per cent slapped on their monthly bill, said NDP Leader Andrea Horwath.

"The HST does not conserve energy, the HST does not help the province in any way in terms of green energy goals," she said.

"The HST is just more salt in the wound for people whose hydro bills are going up, and we think the government can make a real difference here."

Ontario merged the eight per cent provincial sales tax with the five per cent GST on July 1, which increased the cost of many items that weren't previously subject to the provincial levy.

Eliminating the provincial portion of the HST on hydro bills would save families with two or more children about $135 a year, she said.

It would also cost Ontario's treasury about $500 million a year, but the government could cancel some of its promised corporate tax cuts to make up for the lost revenue, Horwath added.

Her party has launched a website -- www.HSToffHYDRO.com -- and Horwath is planning to tour the province to promote the cause.

But the proposal fell on deaf ears in the legislature, where Premier Dalton McGuinty ducked calls to provide the HST exemption.

"We're going to continue to work hard with our families to help them manage these costs," he told the legislature.

"What I will tell you is that we're not going back to a time when our electricity system was characterized as being weak, unreliable and dirty."

Energy Minister Brad Duguid punted the question to absent Finance Minister Dwight Duncan, who was in Sudbury for a government event.

"What we need to do is work with Ontario families -- and we are -- to assist them in addressing the challenges that come with increasing energy rates," Duguid said.

"We cannot stop the investments as the opposition would have us do. They want to return us back where the energy system was many years ago when the Tories were in power. It was a weak system, it was unreliable and it was dirty."

Asked what further help the government planned to provide to help offset rising energy costs, Duguid pointed to energy tax credits announced in last spring's budget.

The northern energy tax credit, for example, provides up to $130 a year for single people and up to $200 for families.

But former NDP leader Howard Hampton, who represents a sprawling riding in northwestern Ontario, said it isn't doing much for pensioners who are subsisting on a diet of bread and margarine because their hydro bills keep going up.

"The premier needs to know that his so-called northern energy credit isn't covering the one-month increase in people's hydro bills, never mind the other 11 months," Hampton told the legislature.

The NDP's call for an HST exemption is a good start, but it doesn't go far enough, said Progressive Conservative Leader Tim Hudak.

The Opposition leader said he'd look at the underlying problems that are driving up hydro rates, such as the government's decision to install smart meters in people's homes and force them into more expensive time-of-use pricing for electricity -- often at rates nearly double what they were paying 24 hours a day until recently.

"I think it's a good day in Ontario when even the NDP has joined the PC cause for lower taxes for families in the next campaign," he said. "It's just too bad that Dalton McGuinty doesn't get it."

Both opposition parties have been hammering the Liberals over soaring hydro bills -- a hot-button issue they believe will continue to plague the government ahead of next year's provincial election.

The Ontario New Democrats seem to be taking a page from the playbook of their successful Nova Scotia cousins, who promised to eliminate the provincial portion of the HST on home electrical bills during the 2009 election campaign.

The party, led by Darrell Dexter, won the race and formed the first NDP government in Atlantic Canada.

Horwath, whose party governed Ontario for a tumultuous five years in the early 1990s, said she'll include the promise in her election platform if the Liberals heed her calls to take the HST off hydro bills.