Dan Gagnier's sudden resignation from the Liberal campaign hounded party leader Justin Trudeau again Friday, as he insisted that the former campaign co-chair's connection to the energy sector was known publicly for months and that he left the Liberal campaign less than 24 hours after an "inappropriate" email to pipeline company officials surfaced.

Gagnier resigned as co-chair earlier this week after an email he wrote to TransCanada Corp., a company involved in the controversial proposed Energy East pipeline, advising several high-level employees on how to effectively lobby a government to have the pipeline project approved.

During a campaign stop in Mississauga, Ont., this morning, Trudeau was for the second day peppered with questions from reporters about whether Gagnier's involvement in his campaign was ethical, and if the incident calls into doubt Trudeau's own ethics.

Dan Gagnier

Dan Gagnier's work as a lobbying consultant for TransCanada Corp. was known publicly for months, Justin Trudeau said Friday. (liberal.ca)

The Liberal leader insisted that he took immediate action when the email surfaced and Gagnier resigned, despite the party's initial insistence that Gagnier had not broken any rules or laws. 

Trudeau said he had wanted Gagnier on his campaign team because he believes in surrounding himself with advisers and volunteers with a wide range of experiences and perspectives, adding that any prime minister should strive to have a diverse group of people surrounding him.

"We ensured from the very beginning of our campaign that we were compliant with all rules and regulations involving consultants and people of that sort, across a spectrum," Trudeau said.

"And when it came to light that one of our volunteers — a senior volunteer, obviously —had engaged in an inappropriate activity, we took responsibility for it."

Trudeau didn't, however, acknowledge or explain the party's initial declaration of support for Gagnier in the hours after the story broke. He also dodged two questions on whether he would further investigate Gagnier or other members of his team for inappropriate actions.

Trudeau did use the opportunity to criticize Conservative Leader Stephen Harper, saying he has resolutely failed to surround himself with a diverse group of advisers and aides because he wants to make all decisions himself. 

Harper, however, said during a campaign event in Quebec City that Gagnier's departure recalls the legacy of the Liberal sponsorship scandal.

"There is no other party in this election that is accused of the things the Liberal Party and Mr. Gagnier have done — that is for them to answer to," he said.

Harper: "It's about the Liberal Party"0:31

"It is the old culture of the sponsorship scandal. It's not about anybody else. It's about the Liberal Party," he continued, adding that the Tories have a "very strict code of ethics."

NDP Leader Tom Mulcair, who spent the morning campaigning in Lac-Mégantic — the rural town about 95 km east of Sherbrooke that was devastated by an oil train explosion in July 2013 — echoed Harper's criticism that Gagnier's resignation recalled the sponsorship scandal, saying it was another example of the Liberal legacy of abusing power.

"This is the same Liberal party — they haven't changed. The party of privilege, the party of entitlement, the party that wants to make itself and its friends rich on the backs of Canadians."

Mulcair added that having a co-chair who was traveling on the campaign plane and active in the war room while working to advance the interests of private company is "unique" to the Liberals.

"No other campaign has been in that situation and I have seen no suggestion that there has been in any other campaign other than the Liberal campaign," he told reporters after announcing the NDP's pledge to strengthen rail safety.

The NDP has already produced advertisements focused on the Gagnier affair that are set to run in English and French on TV and online. 

Mulcair: "This is about what the Liberals do"1:32

It is not uncommon for lobbyists to hold high-level campaign positions during elections. For example, NDP senior campaign adviser Brad Lavigne worked at the Ottawa-based lobbying firm Hill & Knowlton but stepped away from the firm in May to focus on the NDP campaign.

The Liberals said Friday, however, that Lavigne had lobbied for the Canadian Fuels Association — a group that includes Shell Canada, Suncor Energy Projects and as many as 92 other companies — as recently as Sept. 24. The NDP denied the claim, saying Lavigne ceased lobbying for that group in 2014 but the Ontario registry of lobbyists failed to act on his de-registration. 

In his job as a lobbyist and consultant, Gagnier was providing advice to clients in his leadership position throughout the campaign. He had been a consultant for TransCanada Corp since the spring of this year. 

Despite the prevalence of the practice during election campaigns, the NDP has written to the Commissioner of Canada Elections, seeking an investigation into "the possibility of a contravention of the Elections Act, by either or both of the Liberal Party of Canada, and/or TransCanada Corporation." The letter states that Gagnier may have contravened the Elections Act as well. 

Trudeau was in Mississauga to highlight his party's plan for seniors. He was introduced by longtime former Mississauga mayor Hazel McCallion, who also plays a role in the Liberals' most recent campaign advertisement aimed at seniors. 

He told the audience that the Tories' constant efforts to mislead seniors on the Grits' campaign platform was a sign of desperation. 

"They know they can't win a fair fight, so they go for the low blow," Trudeau said. 

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With files from The Canadian Press