Canada has barred entry to UK MP George Galloway because he recently spoke about providing financial support to Palestinian group Hamas.
Mr Galloway, who says he is not a supporter of Hamas has said he will appeal the ban.
The Respect Party leader and MP for Bethnal Green and Bow in London, described the ban as "idiotic".
The BBC's website reported Mr Galloway as saying: "I am not a threat to Canada's national security. I'm just a politician with a different point of view to the Canadian government," he said.
"But, one way or another, I will be heard by those who want to hear me in Canada."
Alykhan Velshi, spokesman for Immigration Minister Jason Kenney, said the decision was originally made by Canadian bureaucrats, but that Kenney would not overrule it in light of Galloway's backing for the Palestinian group Hamas.
"The minister will not give a special exemption from Canada's security laws to Mr. Galloway, nor will he provide special treatment to a man who brags about giving financial support to Hamas, a banned terrorist organisation in Canada, or who offers sympathy for Canada's enemies in Afghanistan," Velshi said.
"I'm sure Mr. Galloway has a large Rolodex of friends in regimes elsewhere in the world willing to roll out the red carpet for him. Canada, however, won't be one of them."
The Canadian Jewish Congress said Galloway was clearly a risk to Canadians for his "moral and, in some cases, financial support for internationally recognized terrorist organizations."
Canada's left-leaning New Democratic Party attacked the government decision as a restraint on free speech.
The move to ban Mr Galloway comes the week he travelled to Gaza at the head of a humanitarian convoy. He praised the Palestinian "resistance" and condemned Israel's 22-day offensive launched in December, in which 1,300 Palestinians died, as "genocidal aggression."
The MP also donated thousands of dollars and dozens of vehicles to the Hamas-run government in the Gaza Strip.
Galloway was formerly a Labour member of Parliament in Britain, but was expelled from the party for urging British soldiers not to fight in Iraq. He subsequently formed his own party, Respect, and was reelected to the House of Commons.