A Civil Service recruitment event was cancelled after Home Secretary Theresa May discovered it had been planned jointly with a student organisation she previously described as "complacent" in tackling extremism.
The Civil Service Fast Stream careers and skills session was due to take place on Tuesday organised with the Federation of Student Islamic Societies' (Fosis) careers section.
In June, the government's reworked Prevent counter-terror review said Fosis had "not always fully challenged terrorist and extremist ideology" and Mrs May rebuked the group.
Around six of the 35 people due to attend had used their Facebook profiles to support terror suspect Babar Ahmad, who has spent seven years in UK high-security prisons while fighting extradition to the United States.
Mrs May was allegedly "furious" when she heard about the event and it was cancelled shortly after.
But Nabil Ahmed, Fosis president, said the cancellation was "incredibly disappointing and confused" and called on the Home Secretary to apologise.
He later wrote a blog for the New Statesman in which he said the cancellation had been arranged "from the darker corners of government".