TORONTO -- The Ontario Lottery and Gaming Corp.'s plans to build new casinos must be halted, given that the property values of some of its existing gaming venues have plunged, the New Democrats said Monday.

The casinos -- including those in Windsor, Sault Ste. Marie and Niagara Falls -- are worth far less today than they were four years ago, said NDP finance critic Michael Prue.

Nearly $260 million in value has been wiped off the books at five Ontario casinos, according to the Municipal Property Assessment Corp.

The property value of the casino in Sault Ste. Marie has dropped $12 million or 50 per cent from 2008, Caesar's Windsor has dropped $40 million or 20 per cent, and Fallsview Resort in Niagara Falls has dropped $173 million or 38 per cent, according to MPAC.

That's devastating for municipalities that rely on property tax revenues from the casinos, said Prue.

"Why won't this government admit that its OLG privatization expansion plans are in total shambles?" he asked in the legislature.

Premier Kathleen Wynne defended the plan, saying the OLG wants to build new casinos because the ones close to the U.S. border aren't bringing in as much money as they did a decade ago.

But she didn't comment directly on the significant drop in property values.

"The job of the OLG is to modernize and to move along," Wynne said in the legislature. "That's what the transformation is about."

OLG's expansion plans have come under fire in recent weeks, prompting the premier to intervene.

Last week, she called in Paul Godfrey, chairman and CEO of the lottery corporation, to make it clear she doesn't want to see any special deals for Toronto to host a new casino.

There were reports that OLG promised Toronto a special agreement that was far more lucrative than what's being offered to other cities who want a casino.

Godfrey denied there was any special deal for Toronto, but said OLG will be rewriting the formula to meet Wynne's wishes that all cities and towns be treated exactly the same by the corporation.

Prue said there's still "mass confusion" over the new casinos and their impact on both municipalities and existing casinos.

When the OLG unveiled its plan a year ago to expand gambling in the cash-strapped province, it tried to assuage concerns that building new casinos in cities like Toronto or Ottawa could cannibalize business from existing facilities.

The plan included shutting down its slot machine operations at racetracks -- which has also come under fire -- and closing or relocating "underperforming" gaming facilities in favour of opening new ones closer to potential customers, such as in Toronto.

Finance Minister Charles Sousa said border casinos have had "some tough times" in recent years.

"The strategy then is to find ways to minimize the degree of cannibalization that occurs in those communities, so we can maximize the value of those casinos," he said outside the legislative chamber.

"And with some of the restructuring and some of the attention being given to them, to also attract more members from the U.S. as well to come ... to those respective markets."