The Harper government is passing legislation that exempts a new Windsor-Detroit bridge from a slew of environmental laws in order to shield it from any legal action U.S. opponents of the project might launch.

Prime Minister Stephen Harper signed a deal in June with Michigan to build a second bridge through Canada's most important trade conduit, but the U.S. operator of the existing Ambassador Bridge between Windsor, Ont., and Detroit fiercely opposes the plan.

Manuel (Matty) Moroun, chief executive officer of the private company that owns the bridge, has said a second one is not needed right now because traffic volumes on his span are down 40 per cent from before the Sept. 11, 2001, terrorist attacks.

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The Canadian government said it anticipates Mr. Moroun or allies would launch legal action in Canada challenging environmental approvals for the new international crossing – and that is why it is heading him off.

The Conservatives introduced new legislation on Thursday – sandwiched inside an omnibus budget bill – that says the Fisheries Act, the Navigable Waters Protection Act, the Species at Risk Act and big parts of the Canadian Environmental Assessment Act "do not apply to the construction of the bridge, parkway or any related work."

"This legislation will ensure that the project will not be subjected to lawsuits on the Canadian side related to the issuance of regulatory permits or approvals and that the project will be constructed without delay or stoppage," Transport Canada department spokesman Mark Butler said.

The Conservatives are defending the measures in the "Bridge to Strengthen Trade Act" as an economic necessity.

The Tories insisted on Thursday that companies building the bridge and related interchanges will be expected to comply with "the intent of all federal laws pertaining to environmental protection" and file action plans to the relevant Conservative ministers.

The government said it already conducted an extensive environmental assessment study of the bridge project in co-ordination with the United States and Ontario.

A second span across the Detroit River is the Harper government's No. 1 infrastructure priority. Close to 30 per cent of annual Canada-U.S. trade moves through the Windsor-Detroit corridor, and Ottawa is worried about bottlenecks and traffic growth over the next 20-plus years.

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The new crossing would be built about three kilometres south of the Ambassador Bridge, which has been operating since 1929.

About $120-billion (U.S.) worth of goods cross the border at Detroit-Windsor annually, carried mainly by the 2.7 million trucks that use the Ambassador Bridge every year. Truck crossings are expected to more than double by 2035.

A Canadian government source speaking on condition of anonymity said Mr. Moroun and his family remain a potential obstacle to building the second bridge.

"One of the biggest concerns we have is there could be further legal action launched by the Morouns or another company controlled by them," the source said.

Canada is so keen for the bridge it has agreed to pay Michigan's $550-million share of the new bridge-related infrastructure costs – which would later be recouped from toll revenue.

The operator of the Ambassador Bridge has waged a public campaign against the project. A spokesman for the Morouns said he could not immediately comment on Ottawa's legal tactic.

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Windsor MP Brian Masse, a New Democrat and a big supporter of a new bridge, said the Tories should still require the project to follow the regular environmental approval process. "It goes over one of the most important fresh waterways in the world, so there is no reason not to do it with full accountability," said Mr. Masse, critic for Canada-U.S. border relations.

The Globe and Mail reported in December, 2011, that Ottawa was considering using an Act of Parliament to insulate the new bridge from legal challenges. Briefing books for Transport Minister Denis Lebel obtained under access to information law suggested the measure was necessary.

The new bridge is expected to cost nearly $1-billion and will be privately financed by the company that builds it. Both countries, however, must put in place customs plazas and ramps and connecting roads – infrastructure that will cost about $2.5-billion.