Mr Tatchell has previously voiced concerns over imams and rappers
Gay activists are angry at the visit to a London university of an Islamic preacher who allegedly endorses the killing of homosexuals.
Abu Usamah was recorded by Channel 4 saying gay people were "dogs" and that they should be "thrown off a mountain".
He is due to speak at at University College London (UCL)next week.
Gay campaigner Peter Tatchell called it "utterly disgraceful". The university said Mr Usamah had been invited to speak by students.
In 2007, the Channel 4 programme, Undercover Mosque, recorded Mr Usamah saying: " Do you practise homosexuality with men? Take that homosexual man and throw him off the mountain."
The preacher has said his comments were taken out of context by the film-makers, and that he was explaining it was an option featured in some books that he did not support.
Earlier this month Mr Usamah gave a speech at City University. Both of his invitations to speak have come from student Islamic societies.
A spokesman for City University's Gay Society said: "Providing publicity for extremists who preach hate risks not just freedom of speech, but all human rights.
"Inviting an extremist who has expressed offensive views about homosexuals, women and non-Muslims to our campus is morally and ethically wrong."
Mr Tatchell said: "The university would never allow a lecture by a white supremacist who used racist abuse and advocated the murder of black people. Why the double standards?"
Mr Tatchell also called on the vice chancellor of City University to resign.
A City University spokesman said: "Our Islamic Society applied for permission to host Abu Usamah through the normal procedures.
"The university then considered its obligation and found no proven reason to decline this event."
A spokeswoman for UCL said the union is autonomous and it was the students' choice to invite the preacher.