An American education professor, one of the founders of a radical 1960s group known as the Weather Underground, which was responsible for a number of bombings in the United States in the early 1970s, was turned back at the Canadian border last night.

William Ayers, a professor of education at the University of Illinois-Chicago and a leader in educational reform, was scheduled to speak at the Centre for Urban Schooling at University of Toronto's Ontario Institute for Studies in Education. But that appearance has now been temporarily cancelled.

"I don't know why I was turned back," Ayers said in an interview this morning 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. To me it seems quite bureaucratic and not at all interesting ... If it were me I would have let me in. I couldn't possibly be a threat to Canada."

Ayers made headlines this summer after Republican vice-presidential candidate Sarah Palin suggested that then-Democratic presidential candidate Barack Obama hung around with domestic terrorists like Ayers. The professor had hosted a meet-the-candidate event at his home for Obama in 1995, during his run for the state Senate. They also worked together on Chicago school reform and served on a charity board together.

Ayers first rose to notoriety in the early 1970s with the Weather Underground. The group claimed responsibility for bombings at the U.S. Capitol, a Pentagon restroom and New York City police headquarters. In 1970, a townhouse in New York the group was using to build a bomb blew up.

Nowadays, Ayers is known more for his work in educational reform. He has written or edited more than a dozen books — including his 2001 memoir Fugitive Days — and travels around the world giving lectures on education.

Jeffrey Kugler, executive director of the Centre for Urban Schooling, is deeply disappointed in the turn of events. For him it's a question of academic freedom. "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. "It seems ridiculous that one university can't have a professor from another university to come and give a lecture on an important educational topic."

Kugler waited for five hours at the Toronto Island airport for Ayers. He was with a lawyer, but the border guard refused to allow Ayers to see the lawyer.

"The entire four or five hours he was not allowed to have representation at all. To me this is an issue of academic freedom. He could not be a threat to anyone ever. Anyone who knows anything about this man – he's a distinguished scholar at the University of Illinois and he has been involved in education reform over the past 15 years. To imagine in any way he was a threat to Canada is really absurd."