The two leaders were to address students separately in two hostels around the same time tonight on the 25th year of the demolition of the Babri Masjid in Ayodhya.
Swamy was scheduled to speak on the topic 'Why Ram Mandir in Ayodhya?' in Koyna hostel at 9.30 pm, and Karat on 'Reclaiming the Republic' in a programme organised by the JNU Students' Union at the Sabarmati Hostel at 9.00 pm.
"The competent authority has cancelled public lectures/ talks on issues of Ramjanm Bhumi and Babri Masjid on Dec 6 in order to maintain communal harmony, peace and stability on campus," the Dean of Students said in a circular.
Karat said the university had taken a "very undemocratic step" in not allowing the talk on the anniversary of the demolition of the 16th century mosque.
"Disallowing discussions is totally against the traditions of JNU," Karat, himself an alumnus, told PTI.
Swamy's official Twitter account re-tweeted a netizen's post that said, "JNU hypocrisy. Allowed terrorist Afzal Guru's death anniversary! Cancelled talk on RamMandir By Dr Swamy!".
The BJP MP's talk was organised by a students' body, the Vivekananda Vichar Manch. One of the organisers, JNU student Prachi Singh, said the forum had been given permission on November 27 to hold the public lecture.
"Yesterday at around 4 pm we got a notice saying the administration had cancelled the event. We had little time to take up the issue as the office closes at 5 pm. We are still awaiting a proper explanation," Singh told PTI.
She said the Vivekananda Vichar Manch was not a political outfit, but an open body which conducts book fairs and blood camps, among other activities.
JNU Teachers' Association president Ayesha Kidwai said a university was the place for democratic discussions on the "most undemocratic of acts".
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)