More than 400 students have signed a petition calling for him to be removed from teaching.
The petition claims that John Finnis has "a long record of extremely discriminatory views" against many people, including members of the gay community.
The protest was sparked by an assertion in a paper, published in 1994 and reprinted in his collected essays in 2011, in which he said that homosexuality is "never a valid, humanly acceptable choice and form of life".
It is "destructive of human character and relationships", he wrote, because "it treats human sexual capacities in a way which is deeply hostile to the self-understanding of those members who are willing to commit themselves to real marriage".
The 78-year-old Roman Catholic, who is emeritus professor of law and legal philosophy at University College, has rejected the criticisms, insisting that he had "absolutely" no hatred for homosexual people.
He told BBC Radio 4's Today programme that the same paper said "exactly the same thing" about what he termed "freewheeling heterosexual sex life", such as premarital sex, extra-marital sex and adultery.
In a summary included in the 2011 reprint, he said he made clear his view that people who "accommodate" heterosexual behaviour of this kind but support restrictions on homosexuality were "morally inconsistent" in a "deplorable" way.
Prof Finnis described the criticisms against him as "a mixture of muddle and misrepresentation".
The paper in question was a testimony to a 1992 referendum on anti-discrimination laws in the US state of Colorado, he said.
"When I reprinted it, I included a summary right at the end and the summary ends by saying that those people who wink at heterosexual lifestyles of a free-wheeling kind and on the other hand support particular restrictions on homosexuals are morally inconsistent, they are discriminatory, they are unfair, and it's a deplorable view," said Prof Finnis.
Asked if he felt any hatred towards homosexual people, he replied: "Absolutely not. I have friends and my family have friends. We benefit from them. They are good people and hatred is not on the scene."
In 40 years of university life, he said "in my private life and my professional life I've been well treated by people of homosexual inclination or living arrangements, very well treated by friends, by colleagues, by members of my faculty, and I've reciprocated".
And he added: "It's a matter of personal pride for them and for me and a matter of professionalism for them and for me that we don't discriminate in our attitudes, we don't criticise people for their faith."
Rejecting claims that his involvement in teaching at the university was discriminatory to people who would not feel comfortable attending his classes, he said that none of the courses he taught were compulsory.
"It's a mixture of muddle and misrepresentation," said Prof Finnis. "I'm no longer employed by the University, but I do teach at the invitation of the faculty in graduate seminars.
"No-one has to do that course or go to the seminars that I do with colleagues in the law faculty."
Oxford University has defended its academics' right to free speech, but also says that it doesn't tolerate any form of harassment.
A spokesperson told us: "We are clear we do not tolerate any form of harassment of individuals on any grounds, including sexual orientation. Equally, the University's harassment policy also protects academic freedom of speech and is clear that vigorous academic debate does not amount to harassment when conducted respectfully and without violating the dignity of others."