TORONTO - Ontario families will end up paying hundreds of dollars more at the pump once the new harmonized sales tax kicks in July 1, the NDP warned Monday.

The average family with at least two children will pay $232 more a year to fill up their car, according to figures calculated by the party using a Statistics Canada economic model.

The government will collect $895 million through new taxes on gasoline when it merges its sales tax with the federal GST, said NDP Leader Andrea Horwath.

"That's on top of the new taxes just to turn on the lights," she told the legislature. "That's on top of the new taxes just to turn on the heat and keep the house warm."

Taxpayers have plenty of information from the government about how the HST will affect them, including the 600,000 new jobs it's expected to create, said Premier Dalton McGuinty.

"Fortunately, there will come a time very, very shortly when the rage associated with the rhetoric will abate and our new tax reforms will become the reality," he told the legislature.

"Then people will have an opportunity for themselves to imagine and to experience exactly what is happening as a result of our changes."

The HST isn't the only money grab, said Opposition Leader Tim Hudak.

The average family has been paying $2,700 more a year in new taxes and fees on everything from tuition to electricity bills since 2007, when the Liberals won a second majority government, he said.

"This simple basket of goods and services we all use every day is becoming unaffordable under the McGuinty government," he said outside the house.

Revenue Minister John Wilkinson said drivers will see an eight per cent hike at the pump when the HST takes effect, because taxes are built into the price per litre.

"When we harmonize our sales tax, it means that about 17 per cent of the things that we buy every day are going to see an increase in the sales tax," he said.

But the new revenue will be used to cut income and business taxes by $10 billion over the next three years, Wilkinson added.

The NDP released figures last week that suggest families will pay hundreds, if not thousands of dollars more in taxes once the single sales tax takes effect.

The party calculates that the average Ontario family will pay $794 more in taxes every year if businesses don't pass on their savings to consumers, and $638 a year more if businesses do lower prices to reflect lower input costs.

The governing Liberals are offering one-time payments of up to $1,000 for families and $300 for singles to offset the initial impact of the HST.

McGuinty pointed out that the HST has received the support of both the NDP government in Nova Scotia -- which is hiking the tax to 15 per cent from 13 per cent -- and such prominent Conservatives as former premier Mike Harris and federal cabinet ministers Tony Clement and Jim Flaherty.