Michael Chan says it is "ludicrous" and "totally false" for Canada's spy agency to believe he may be susceptible to influence from the Chinese government, while the CSIS affair deepened a rift between Ottawa and Ontario.

In an open letter Wednesday, Ontario's Minister of Citizenship, Immigration and International Trade hit back at the concerns of the Canadian Security Intelligence Service, revealed this week by The Globe and Mail.

"There is a persistent theme that there is a perceived risk that I am under undue influence and that I am an unwitting dupe of a foreign government," he wrote. "This is offensive and totally false. This personal attack is deeply offensive to me and to my family." He added that "nothing I have done in any way supports any suggestion that I am a possible threat to Canada or to Ontario."

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Mr. Chan's defenders lined up to criticize CSIS and the federal government's handling of the matter. Some called on Justice Minister Peter MacKay to apologize for suggesting Mr. Chan was part of an "ongoing investigation." Premier Kathleen Wynne redoubled her defence of Mr. Chan, calling him a man of "sterling character" who had landed nearly $1-billion worth of investment from Chinese companies during a trade mission to China last fall.

As The Globe revealed this week, CSIS was concerned the minister was too close to the Chinese consulate, prompting a senior official to formally caution the province about the minister's alleged conduct in a briefing that took place in 2010.

Officials in then-premier Dalton McGuinty's office deemed the allegations baseless, but it is unclear what they did to investigate. Mr. Chan has denied he asked for the consul's intervention on his visa and that he owns property in China. He has not denied that he was in regular contact with the consul.

In a statement, Ms. Wynne suggested the activities that CSIS found suspicious were merely Mr. Chan's attempt to keep close ties with his former country.

"There are some who may believe that there is something sinister about maintaining deep ties with one's country of origin, or one's culture," she wrote in a statement. "I believe the opposite and so do millions of Canadians who have immigrated to Canada."

Ms. Wynne has said she did not learn of CSIS's suspicions until The Globe started asking about them last year. Her office on Wednesday suggested that she did not ask for the matter to be investigated, and is simply taking Mr. Chan and Mr. McGuinty's staff at their word that the concerns were without foundation.

"No concerns have ever been brought to the current Premier's Office by CSIS or any relevant authority," her spokeswoman, Lyndsay Miller, wrote in an e-mail.

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Mr. MacKay said on Tuesday Mr. Chan was part of an investigation, while providing no details on what it entails or who it is targeting. "Clearly there are people outside our country, as inside our country, who would seek to exert influence," he said.

The Globe had reported that Mr. Chan was never under formal investigation by CSIS.

Dwight Duncan, who was Ontario's finance minister and deputy premier at the time CSIS brought the allegations against Mr. Chan to the province, said Wednesday that they were not discussed at the cabinet table and he was not made aware of them. Mr. Duncan said he was only aware of the general claim made publicly by then-CSIS director Richard Fadden that some politicians were under foreign influence. For all he knew, Mr. Duncan said, Mr. Fadden's comments "didn't have to be [about] a Chinese national," noting that in his role as the province's treasurer, he had meetings with China's ambassador and its bank executives.

Mr. Duncan took aim at CSIS for what he called a "smear" against "one of the most decent, honourable people I know," and said the agency's handling of the issue was "like Keystone Cops." He also had harsh words for Mr. MacKay. "The Attorney-General of Canada, to publicly come out like that?" he said. "It's mind-boggling."

Liberal MP John McCallum, who represents the federal equivalent of Mr. Chan's seat, called on Mr. MacKay to apologize in the House of Commons.

"I've known him for 15 years and he's a patriotic Canadian," the MP said, adding Mr. MacKay's statements "were beneath the dignity" of his office. "The Attorney General acted totally inappropriately in referring to an operational matter and he should apologize."

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Mary Ann Dewey-Plante, director of communications for Mr. MacKay, refused all comment Wednesday.

In his letter, Mr. Chan echoed Ms. Wynne's language, contending that his purported connections to the Chinese government are no different than any other Canadian keeping ties to their former country.

"Maintaining deep, meaningful connections with one's culture, with one's country of origin, is something millions of Canadians cherish," he wrote, adding: "I came to this country as a young man. Canada welcomed me. While I am proud of my Chinese heritage, I am a Canadian first and foremost. I owe all the success I have had to this country and, most particularly, to the Province of Ontario."