A leading British historian has accused a US university of "colluding in the Sovietisation" of Roman Catholic intellectual life after it rescinded an invitation to a prominent liberal theologian who has argued the case for same-sex marriage on the grounds that she "dissent[s] publicly" from the Church's moral teachings.

Tina Beattie, director of the Digby Stuart Research Centre for Catholic Studies at Roehampton University, was one of 27 theologians, clerics and activists who earlier this year wrote a letter to the Times arguing that Catholics could, "using fully informed consciences ... support the legal extension of civil marriage to same-sex couples."

The intervention, in August, prompted an outcry from traditionalists and led to the cancellation of a lecture Beattie was due to give in Bristol.

It has now emerged that Beattie, who had been invited to be a visiting fellow and give public lectures at the University of San Diego this winter, has had that invitation rescinded by the Catholic institution, whose president said Beattie's "public stances" were not in keeping with the campus. The decision, which Beattie learned of last week and which she made public on Thursday, has sparked criticism from theologians on both sides of the Atlantic.

Eamon Duffy, professor of the History of Christianity at Cambridge, has urged the university to reconsider. "It is deeply dispiriting that the president of a Catholic university should characterise academic discussion and debate among Catholics as 'dissent', and should seek to suppress academic exchange by black-balling an individual whom the church has not condemned," he wrote in a letter to the university's president, Mary Lyons.

Comparing her stance unfavourably with that of Cardinal Newman, who "deplored similar attempts to silence discussion in the church", he concluded: "I fear that by publicly withdrawing this invitation, the University of San Diego has brought academic ignominy on itself, and is colluding in the Sovietisation of Catholic intellectual life which many feel is one of the saddest features of the contemporary church."

Beattie said that, while the exact reasons for the cancellation of her San Diego visit have not been given, she had been the target of an online "blog campaign" by her critics ever since the letter in the Times, and that the controversy had spread to the US. The Clifton lecture, she added, had been cancelled following an outcry by protesters and a subsequent intervention by the Congregation for the Doctrine of the Faith (CDF), the body which oversees Catholic doctrine and is seen by many as having become more authoritarian under Pope Benedict XVI, as well as less tolerant of aspects of the Catholic Church for England and Wales.

"I think it's a really important time for the Church in this country because we have so far been not divided by this kind of ugly rupture," Beattie told the Guardian, calling on the Catholic Bishops of England and Wales to show a "very strong united front" in the face of any attempt to stifle dissent. "There's been a creative atmosphere of people being able to hold different positions in this country without it causing this kind of ugliness and I really think it's vital that the Bishops collectively stand up to protect that now."

The row over Beattie comes amid reports that the prefect of the CDF, Archbishop Gerhard Ludwig Mueller, intends to clamp down on the pastoral provision - supported by Archbishop Vincent Nichols - given to gay Christians by the so-called Soho Masses in London. The German magazine Katholishches reported last month that Mueller, who was appointed by the pope in July, was determined to tackle the services, which are a unique and much-cherished feature of the gay community.

In an email to Beattie, Lyons said that the invitation to be a visiting fellow at the university's Frances G Harpst Center for Catholic Thought and Culture was being rescinded "after great and thoughtful consideration" because of what was deemed the contradiction between Beattie's beliefs and the centre's mission. "This [fellowship] would include clear and consistent presentations concerning the Church's moral teachings, teachings with which you, as a Catholic theologian, dissent publicly," she added.

On her blog, Beattie said: "The cancellation of my visit is not the most important issue in all this. The real issues are academic freedom, the vocation of lay theologians in relation to the official magisterium, and the power of a hostile minority of bloggers (some of whom are ordained deacons and priests) to command the attention and support of the CDF. The latter is the most sinister development of all, and it is a cause for scandal which brings the church into disrepute. However, it also shows how deep this crisis has become."