The DUP says it has made a formal complaint against an academic who wrote an email claiming the party may have been responsible for gay and lesbian young people killing themselves.
A DUP MLA confronted Dr Graham Ellison of Queen's University at a meeting of the Stormont justice committee.
The meeting concerned a Bill on human trafficking, sponsored by a DUP MLA.
Jim Wells said he had seen an email written by Dr Ellison to a woman who had given evidence for the Bill.
If the Bill, sponsored by Lord Morrow, is passed, it would make it illegal to pay for sex in Northern Ireland.
In the email, Dr Ellison said: "Why have you hooked yourself up to that lot in the DUP? Have you any idea what they stand for in terms of social issues around women's rights; women's reproductive rights issues and so forth?
"In terms of gay and lesbian politics that I have an interest in, they are one of the most repressive and socially backward parties you could imagine."
Mr Wells said in the email Dr Ellison, who admits writing it, used a swear word that he would not repeat in public.
But the email said: "Who knows how many gays and lesbian young people in Northern Ireland have committed suicide because of this bloody party.
"I could also remember not long ago, five or six years, that the party, i.e. the DUP, was claiming that rape within marriage was impossible. They are simply latching onto this idea about sex that it is grounded in biblical teaching and not in feminist theory."
He put it to the academic, who is a member of the QUB's School of Law, that his opposition to the clause in the Bill banning prostitution was because of his prejudice against the DUP.
Dr Ellison replied: "Actually, it is nothing of the sort."
He said he was trying to reason with the woman believing he could "talk her round".
He denied the content of the email was abusive and claimed there was an "element of moral crusade" behind the Bill.
Dr Ellison said he was not convinced that the Trafficking Bill was “in the best interests of the country".