NDP MP Nathan Cullen speaks to reporters at the site of the proposed Enbridge bitumen terminal on Douglas Channel, south of Kitimat, B.C., during the NDP's tour of resource development sites in northwestern B.C. in June. (Robin Rowland/Canadian Press)

The NDP's House leader claims the government is trying to shut him up when it comes to questioning federal bureaucrats at the joint review panel looking into Enbridge's Northern Gateway pipeline proposal.

Nathan Cullen's request to cross-examine officials from the departments of the environment, natural resources, transport and fisheries and oceans was met by a letter from the Department of Justice asking the panel to deny his appeal.

"It's a bit of an intimidation tactic," says Cullen. "All along, if you've been opposed or raised concerns about this pipeline, Mr. Harper's government has called you a radical or an enemy of the state. These are all tactics to say 'you're just going to have to accept what we tell you to accept.'"

Natural Resources Minister Joe Oliver, in an email to CBC News on Wednesday afternoon said, "Cullen is seeking to politicize the work of the panel instead of waiting to hear the independent experts report."

Cullen is an intervener at the review. As such, he is allowed to question government and Enbridge witnesses at the hearings.

The Department of Justice does not argue that right. In the letter to the panel, Kirk Lambrecht, the general counsel for the Prairie Region, raises concern about the subject matter of the questions Cullen wants to ask.

He said Cullen's questions don't deal with "evidence that has been submitted by other parties during the joint review process." And that contravenes the panel's hearing order, or rules of play.

Questions for 4 different departments

Cullen wants to ask Environment Canada about its new, versus old, environmental assessment criteria. The Canadian Environmental Assessment Act was completely overhauled in the spring.

His line of questioning for Transport Canada would deal with the independence of the review process and regulations on diluted bitumen (oilsands oil) compared to conventional oil.

From Natural Resources Canada he is looking for answers on overseas project promotion and carbon pricing. Finally, Fisheries and Oceans would field his questions about the Fisheries Act, habitat protection and water crossings along the pipeline.

"To allow such questions would undermine fairness to the witnesses, delay the proceedings and would not assist the panel in its assessment of the application," wrote Lambrecht.

Cullen has a different interpretation of the review's guiding principles. He thinks that any evidence that was submitted or needs to be talked about is open for discussion.

"If what the government is going to do and what the panel's going to do is say, 'If the word doesn't appear you can't ask a question about it,' it would narrow the conversation so much as to make the whole thing ridiculous," says Cullen.

Oliver said "the joint review panel independently makes all decisions respecting its proceedings. Our officials will answer any questions that the independent panel deems relevant."

The MP for Skeena-Bulkley Valley expects to do his questioning at the hearings in Prince Rupert sometime in the next few weeks. The panel doesn't have a timeframe for making a decision on the Department of Justice's letter.