The National Council of Canadian Muslims has filed a notice of libel in the Ontario Superior Court of Justice that accuses Jason MacDonald of acting maliciously when he made the comment earlier this month.
The council had criticized the inclusion of a controversial rabbi in Harper's delegation that went to the Middle East last week.
"Rather than responding to our legitimate concerns, the PMO's director of communications attacked us and attempted to smear our name by claiming NCCM had 'documented ties to a terrorist organization such as Hamas,'" Ihsaan Gardee, the council's executive director, told a news conference Tuesday.
"Nothing could be further from the truth. NCCM will not let the PMO's false statement stand."
The council says MacDonald's comment was a deliberate attempt to discredit the group and Harper is responsible for the words uttered by his spokesman.
The libel notice is the first step in what could become a formal lawsuit.
The Prime Minister's Office responded tersely: "As this matter may be the subject of litigation, we have no further comment."
Further legal action is possible, said Nader Hassan, lawyer for the council.
"Whether we go through with the lawsuit is going to depend on a number of factors, namely the quality, timing and content of the public apology and retraction," he said.
Gardee said MacDonald's comment was "categorically false, offensive and defamatory."
The libel notice said MacDonald's statement was unwarranted.
"The defamatory words were stated maliciously in order to discredit and insult an organization that did nothing other than exercise its constitutional right to freedom of expression to criticize a decision made by the prime minister," it said.
"Mr. MacDonald simply made up that statement in an effort to discredit NCCM and deflect its criticism of Mr. Harper."
The council describes itself as an independent, non-partisan, non-profit group which has worked for 14 years on human rights and civil liberties issues on behalf of Canadian Muslims.
A half-dozen other rights groups, including the Canadian Civil Liberties Association and the Canadian Association of University Teachers, have offered support to the Muslim group.
Farhat Rehman of the Canadian Council of Muslim Women said more than just the council was impacted by the remark.
"This defamation endangers the very valuable work of NCCM and goes against every Canadian democratic principle," she said.
"Further, it exposes the members of NCCM and the whole Muslim community to suspicion, hatred and bigotry."
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