Welsh Secretary Cheryl Gillan has pulled out of a lecture at Aberystwyth University after online reports of protests by students over tuition fees.
The Wales Office said it was told police could not guarantee Thursday's protest would be peaceful, and policing would mean a "large cost".
Last week the Conservatives' London HQ was attacked after a protest about tuition fees turned violent.
Shadow Welsh Secretary Peter Hain criticised her late withdrawal.
Ms Gillan was due to give a speech to the Institute of Welsh Politics at the campus.
Mr Hain said the withdrawal "at the last moment is a total disgrace. I can't ever recall a politician treating a Welsh university with such contempt".
Mr Hain went on: "I know from experience, it is a huge honour to be invited to give the Aberystwyth annual political lecture, one of the highlights of the Welsh political calendar. For her to pull out at the last minute citing security fears is arrogant in the extreme.
"I understand there were peaceful protests planned, and I know students were looking forward to meeting her to discuss her government's plans for higher education.
"I suspect the real reason for her withdrawal is she is scared of facing students who are understandably anxious at the prospect of being saddled with a lifetime of debt, thanks to her government.
"Her behaviour is outrageous. She is not doing the job of secretary of state for Wales. She is letting Wales down, and letting Welsh students down.
"It's beginning to look like Wales will soon be a no-go area for the secretary of state."
A spokesman on her behalf said: "Peter Hain is being irresponsible in his criticism.
"He has not seen the content of the police advice, which is something we take very seriously."
The spokesman said that the Wales Office had been told that to police the event would have needed "significant police resources" and that Dyfed-Powys Police may even have had to bus in officers from other police forces.
The spokesman added that given the events in London last week they "didn't want things to kick off" and that the police "needed to be on the street fighting crime, not protecting the secretary of state".
He added that the Wales Office had been in touch with the university and was keen to reschedule the speech for another time.
Professor Roger Scully, director of the Institute of Welsh Politics, said: "We had very much looked forward to welcoming the secretary of state for Wales to give the annual lecture.
"While we are disappointed that the she has had to postpone her visit on this occasion we very much hope that it might be possible to reschedule the lecture at some point in the near future."