In a letter to the International Relief Fund for the Afflicted and Needy, the RCMP said the federal government had added the group to a list of "terrorist entities" as of April 24.
"IRFAN is now classified as a 'terrorist group' under Canadian law," the letter from Supt. Stephane Bonin states.
"As a consequence, any property or asset belonging to IRFAN is now frozen."
The letter offers no reason for the listing decision but Canada Revenue Agency has said the organization supported Hamas, itself branded as a terrorist organization.
A statement Tuesday from Public Safety Minister Steven Blaney noted CRA's contention — which was to be argued in court next week — that IRFAN provided aid to groups run by officials of, or who supported Hamas.
IRFAN, based in Mississauga, Ont., sent about $14.6 million in resources to "various organizations associated with Hamas" between 2005 and 2009, the statement said.
The non-profit IRFAN was due in Federal Court of Appeal on May 6 to contest a 2011 CRA decision to revoke its charitable status because of its alleged ties to Hamas and failure to keep proper records.
No one for IRFAN was available to comment, but a lawyer speaking for the group condemned the listing as an attack on humanitarian support for Palestinians.
IRFAN did not know the terrorist listing was in the works and had no opportunity to respond or offer its side of the story, Ottawa-based lawyer Yavar Hameed said in an interview.
There's no evidence the group did any direct funding of Hamas, he said.
"This listing happens days before we are to present arguments for the first time to the Federal Court of Appeal, so we're very concerned about the timing with which this listing happens which completely undermines any ability for this organization to work as a charity," Hameed said.
"On its face, we believe it is an unfair and unconstitutional decision that has been taken."
Hameed also said the listing was a "nail in the coffin" for Canadian humanitarian support for "orphans and destitute" Palestinians and wondered if the decision was politically motivated.
Even acting for IRFAN as a lawyer puts him in a "tenuous" position because any support for the group could be seen to run afoul of the Criminal Code, he said, adding it is only the second time a Canadian domestic organization has been listed as terrorist group.
Meanwhile, RCMP said Tuesday it had raided IRFAN's head office in Mississauga and a residence in Montreal as part of a terrorism-financing investigation.
"An extensive amount of documentary evidence along with stored media, money and other records were seized," police said in a statement.
RCMP offered no further details of Monday's raids.
Blaney's statement noted "severe penalties" are in place for those who run afoul of the listing law.
"Canada will not tolerate terrorist activities including the financing of terrorist groups," Blaney said.
"IRFAN-Canada has knowingly financed Hamas, a listed terrorist entity, for many years."
In revoking its charitable status that followed two audits over 10 years, CRA referred to unproven suggestions from the U.S. government that IRFAN had ties to an Hamas-linked American aid group.
It also claims IRFAN "repeatedly misrepresented its fundraising activities to the public" and that the revocation decision was fair and legal.
It was not immediately clear whether the Federal Court of Appeal case against CRA had been rendered moot by Ottawa's listing decision.