CALGARY - An environmental law group is threatening legal action if the Alberta government's inquiry into the funding of oil and gas industry foes continues as is.

Vancouver-based Ecojustice issued the warning in a letter to inquiry commissioner Steve Allan and has given him 30 days to respond.

Alberta Premier Jason Kenney has said deep-pocketed American charities have bankrolled efforts to block Canadian energy development for years.

In announcing the $2.5-million inquiry this summer, Kenney said it would find out if any laws have been broken and recommend any appropriate legal and policy action.

Ecojustice says in the letter there's a reasonable apprehension that the inquiry will be biased against the groups it's investigating.

The group also says the inquiry risks violating rights to freedom of expression and assembly protected under the Canadian Charter of Rights and Freedoms.

Ecojustice adds that the inquiry must be procedurally fair, meaning anyone called before it must be able to cross-examine witnesses and receive copies of documents submitted as evidence, among other things.

It's proposing amendments to the inquiry's terms of reference that would fix some of those issues.

Ecojustice executive director Devon Page likened the inquiry as it stands to a “medieval witch hunt.”

“It wasn't about finding the truth. It was about finding witches,” he said in an interview.

“This is a political exercise. It's intended to target Canadians who are concerned about climate change and silence them.”

The inquiry is one plank of the United Conservative government's strategy to fight back against critics of Alberta's beleagured oil and gas industry, which has struggled to get its product to markets as new pipelines are mired in delays.

Kenney defended the inquiry on a call with reporters from New York on Wednesday where he is visiting with U.S. business leaders. 

"It's entirely predictable," Kenney said while admitting he hadn't yet been briefed on the letter. "It sounds like a regurgitation of the laughable letter from Amnesty International last week." 

"These folks think they should be able to use Alberta as a punching bag." 

When Kenney announced the inquiry, he said it would “serve notice that Alberta will no longer allow hostile interest groups to dictate our economic destiny as one of the most ethical major producers of energy in the world.”

Allan, the commissioner, is a forensic and restructuring accountant with more than 40 years experience. His ability to compel witness testimony and records is limited to Alberta, but Justice Minister Doug Schweitzer has said much of the information Allan needs is publicly available and he'll be able to travel outside Alberta to gather more.

The first phase of the inquiry is to focus on fact finding, with public hearings to follow if necessary. Allan is to deliver his final report to the government next summer.

With files from CTV's Matthew Black