TORONTO — Ontario is delaying plans to build two new nuclear reactors, saying Monday that Atomic Energy of Canada Ltd.'s bid would cost billions more than the province is willing to pay as it hinted federal aid could help seal the deal.

AECL was the only one of three candidates to build the Darlington nuclear station reactors to properly address requirements around assuming responsibility for cost overruns, but that bid was still too expensive, said Energy Minister George Smitherman.

Ottawa, which earlier this year announced plans to put AECL's nuclear reactor business up for sale, may want to step in to allow AECL to make a more competitive bid, he added.

Once the government clarifies the future ownership of AECL, it must "sharpen their pencils substantially so that the people of the province of Ontario can renew their nuclear fleet with two new units from that company," Smitherman said.

"AECL is the government of Canada's company so, absolutely, the government of Canada is in the driver's seat with respect to giving AECL the opportunity to build new reactors in Ontario."

Smitherman wouldn't discuss the price tag attached to any of the offers or give a timeline for how long the postponement will last. He would only say the cost of the proposal was off "substantially, certainly by a measure of many billions."

The announcement comes as a surprise in a province that is spending $26 billion on a major expansion of nuclear power over the next two decades as it aims to generate 50 per cent of the province's electricity with that source.

Smitherman had said just last month that Ontario's plans to choose a company to refurbish its nuclear reactors wouldn't be affected by Ottawa's plans for a sale.

The future of AECL is widely considered to be tied to a successful Ontario bid.

The Organization of CANDU Industries, which represents the companies that would build parts for the new reactors, said Monday it was "extremely concerned" about how the move would impact the more than 30,000 workers in the industry.

"The member companies of OCI have invested heavily in this process and this delay will cause some of them considerable financial difficulty, possibly even bankruptcy," president Neil Alexander said in a statement.

Officials at AECL were not available for comment.

Smitherman insisted the announcement shouldn't be seen a shift away from nuclear, but stressed the province isn't going to build the new plants, expected to be up by 2018, "at any cost."

Steve Outhouse, a spokesman for federal Natural Resources Minister Lisa Raitt, said any discussions about costs rested with AECL, adding there was nothing that would push Ottawa to get involved at this stage.

Critics have said choosing AECL could mean higher costs, noting the price tag for building reactors has more than doubled in the last three years, and taxpayers risk being stuck with the bill.

NDP energy critic Peter Tabuns said Monday's move is an attempt to get a "massive bailout" from Ottawa for possible costs overruns by AECL, and that Smitherman "may be negotiating in public."

"They're going to try to stick us, through the federal budget, with the cost of overruns at this plant," Tabuns said.

The government's decision to put the plan on hold shows how much the costs for building nuclear plants have risen since an estimate of $6 billion in 2005, when Ontario committed to upgrade the plants, Greenpeace energy analyst Shawn Patrick Stensil said.

"This could be a set up for the Ontario government to back out -- with face -- of its 2005 nuclear commitment," Stensil said, noting recent estimates put the costs closer to $15 billion.

"It's also passing the buck if the federal government decides not to lower the price. The McGuinty government can blame the Harper government for killing AECL."

Areva Group of France and U.S.-based Westinghouse Electric Co., who were also in the running to build the reactors, didn't properly address the issue of cost overruns, Smitherman said.

Their bids could be considered in the future if the companies still want to part of process, but Smitherman said AECL is "very well-positioned to come back to us and initiate discussion."

Ontario currently has three operating nuclear plants: Pickering and Darlington east of Toronto, and Bruce on the shores of Lake Huron.

The change will have no impact on Ontario's plans to get rid of coal-fired plants by 2014, nor will it change the energy mix in the province or affect the reliability of electricity, Smitherman said.

Saskatchewan Energy and Resources Minister Bill Boyd said Monday that Ontario's decision to delay its nuclear plans won't derail his province's atomic power review.

Boyd said cost is always an issue, but added that if Saskatchewan pursues nuclear power it would look for a partnership that would not use taxpayer money.