Environmental groups are urging the Liberal government to strengthen its proposed changes to the process of assessing resource projects, arguing the current plan will allow economic development to trump environmental protection.

As the government this week begins the lengthy process of moving the 350-page bill through Parliament, scientists and advocates worry there is no clear guidance under which projects would be turned down because of environmental impacts.

Instead, the minister of environment or, in some cases, the federal cabinet, will have discretion to declare a project to be in the national interest and approve it, regardless of the findings of the impact assessment review.

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"The factors to be weighed by the minister all just seem to be factors," Megan Leslie, president of World Wildlife Fund Canada, said in an interview. "So I don't see anything in here that indicates a 'no go,' that a project won't happen because these are environmental considerations beyond the pale."

Environment and Climate Change Minister Catherine McKenna introduced legislation last week to overhaul the federal environmental assessment review process that covers major resource projects such as pipelines, mines, hydroelectric dams and transmission lines.

The bill would create the Impact Assessment Agency to replace the existing Canadian Environmental Assessment Agency, and put it in charge of major reviews, rather than the current industry specific bodies such as the National Energy Board. The legislation would also impose tight timelines on reviews while making the process more transparent and open to public participation.

Prime Minister Justin Trudeau argues the impact-assessment legislation is needed to restore scientific rigour and credibility to the review process. However, the government will not revisit previous decisions and it could be many years before another big interprovincial oil pipeline is proposed.

In an interview, Ms. McKenna defended the government's call to maintain decision-making in the hands of elected officials rather than the Impact Assessment Agency or reviews panels that would be appointed to handle the most contentious cases.

"Transparency is really important, but ultimately the federal government in difficult cases is going to have to make a decision in the national interest," she said. "And we'll ultimately be held accountable."

The Liberal government has been criticized on all sides for its handling of major pipeline projects since taking office and it faces a bitter interprovincial battle between Alberta and British Columbia over the Trans Mountain expansion project, which it approved 15 months ago. The Liberals were slammed by Conservatives for rejecting the Northern Gateway pipeline and allowing the proposed Energy East project to die, while being condemned by environmentalist advocates and B.C.'s government for approving the Trans Mountain pipeline expansion, which would result in a dramatic increase of tanker traffic in coastal waters.

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Under the proposed legislation, Canadians will be able to assess the evidence the government used to make its decisions – including the recommendations from the review agencies. For the first time, the minister or cabinet will be required to issue reasons for a decision and "not just a press release," Ms. McKenna said.

The factors to be considered include whether the project would cause significant adverse environmental impacts and whether those could be mitigated.

Ms. McKenna said the new system will allow serious environmental obstacles to be identified before a company makes formal application, which may dissuade proponents from moving forward in the most contentious developments. Projects that do not fit within the national climate-change plan will not be approved, she said.

The Liberals took into consideration Alberta's carbon tax and its future cap on oil sands greenhouse emissions when it approved Trans Mountain. Ms. McKenna indicated that, given those provincial policies, Ottawa would not review expansion plans in the oil sands, including the new plans to use solvents to extract bitumen from reservoirs.

However, measures announced to date by federal and provincial governments are not sufficient to meet Ottawa's commitment to reduce emissions by 30 per cent from 2005 levels by 2030, and Ottawa has committed under the United Nations Paris accord to adopt an even tougher target.

The impact-assessment legislation would also allow Ottawa to conduct regional assessment in key areas that would consider the cumulative impacts of development on the environment and the health of local residents.

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However, there is no requirement for Ottawa to conduct regional or strategic assessment, and no clear indication how such studies, when completed, would guide project proposals, said Justina Ray, executive director and chief scientist of Wildlife Conservation Society Canada.