Weather Underground co-founder William Ayers, who made headlines last year during the U.S. presidential race for his controversial links to Barack Obama, was turned back at the Canadian border Sunday night.

The Weather Underground, a radical 1960s anti-Vietnam War group, was responsible for a number of bombings in the United States in the early 1970s.

Ayers, an education professor at the University of Illinois at Chicago, had been scheduled to speak last night at the Centre for Urban Schooling at the University of Toronto's Ontario Institute for Studies in Education.

"I don't know why I was turned back," Ayers said in an interview yesterday from Chicago. "I got off the plane like everyone else and I was asked to come over to the other side. The border guards reviewed some stuff and said I wasn't going to be allowed into Canada. ... If it were me, I would have let me in. I couldn't possibly be a threat to Canada."

The Ayers case couldn't be discussed specifically, said Anna Pape, a spokesperson for the Canada Border Services Agency. But she added that border officers can deny entry into Canada if an individual has been involved in such things as criminal activity, human rights violations or organized crime.

NDP Immigration critic Olivia Chow plans to write Immigration Minister Jason Kenney to get him to grant Ayers permission to return to Canada and give his lecture. Kenney's office referred questions on the case to Minister of Public Safety Peter Van Loan's office. No one from Van Loan's office was available to comment late yesterday afternoon.

Ayers said he has been back and forth to Canada frequently in the past, attending speaking engagements in Ottawa, Toronto and Vancouver. In fact, he said his passport is full of stamps of all the places he has travelled to, including several stamps from Canada.

This, however, isn't the first time Ayers has been refused entry into Canada. In July 2005 he was supposed to give a lecture to teachers at the University of Calgary but was denied entry then.

Ayers rose to notoriety in the late 1960s with the Weather Underground, which claimed responsibility for bombings at the U.S. Capitol, a Pentagon rest room and New York City police headquarters. In 1969 Ayers and others – known then as the Weathermen – were involved in Chicago protests known as the "Days of Rage." Ayers, one of a number of people charged by federal authorities, spent 10 years as a fugitive. The charges against Ayers were eventually dropped in 1978.

Ayers was back in the news in the summer when Republican vice-presidential candidate Sarah Palin suggested that then-Democratic presidential candidate Obama hung around with domestic terrorists like Ayers. Ayers had hosted a meet-the-candidate coffee session at his home for Obama in 1995 during his run for the state senate. They had also worked together on Chicago school reform and served on a charity board together.

Nowadays Ayers is praised for his work in educational reform. Having written or edited more than a dozen books, he was named Chicago Citizen of the Year in 1997 and has advised Chicago's Mayor Richard M. Daley on school reform.

Jeffrey Kugler, executive director of the Centre for Urban Schooling, is deeply disappointed in the turn of events.

"It's kind of ironic the day before Barack Obama is going to become president, this is what the Canadian border security has done," said Kugler, who believes Ayers was turned back because of a 1969 conviction after an anti-war demonstration.

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