Gay Christians are to lobby the government this weekend against attempts by the Church of England to obtain exemption from planned anti-discrimination employment regulations.
They accuse church leaders of sabotaging legislation aimed at outlawing discrimination on the grounds of sexual orientation.
The row is an early challenge for Rowan Williams, the Archbishop of Canterbury, who has already fallen foul of some evangelicals for sympathising with gays.
Barbara Roche, the minister for social exclusion and equality who is responsible for the legislation, will address the annual conference of the Lesbian and Gay Christian Movement (LGCM) in London tomorrow. She will come under pressure to ignore the church's insistence that faith-based organisations should be allowed to bar gays from employment on moral grounds..
A submission to the government earlier this year by the church's archbishops' council - in effect, its executive body - said: "Churches and other faith-based organisations must not find themselves in a position where the law of the land is preventing them from conscientiously applying their own sincerely held doctrines and beliefs on moral issues."
The document was sent to the government before Dr Williams' enthronement in February but, in a sign that the archbishop is treading warily he has decided not to address an LGCM conference later this year.
Groups such as the Evangelical Alliance and the rightwing Christian Institute have attempted to mobilise opposition to the legislation. They claim that the regulations would force churches to employ gays or face legal challenges if they refused.
LGCM members say that if the church succeeds in getting an opt-out, existing jobs would be at risk and churches would become "hostage to the most intolerant and fundamentalist groups within (their) religion".
Richard Kirker, the LGCM's general secretary, claimed in a letter to the archbishop that the church's demand would represent "a carte-blanche opt-out from the rules governing the rest of society".
He said: "The effects could be felt by all minorities, of belief, age and sex as well as by sexual orientation - we ask you to seek the withdrawal of this ill-conceived and unchristian proposal."
The EU directive on which the legislation will be based allows limited exemption for religious organisations to arrange for individual posts to be filled by persons sharing their beliefs, where there is a genuine occupational requirement.
Supporters of the legislation believe that the church's motive is to gain exemptions to allow it to discriminate against gays for all jobs, including cleaners and teachers, whose work does not require them to demonstrate overt religious beliefs.
The issue is extremely sensitive for the Church of England, which has been riven over the question of homosexuality.
Some evangelicals refuse to recognise Dr Williams' appointment because of his perceived sympathy to gays.
He has admitted knowingly ordaining a gay priest earlier in his career but has said that he will not allow his personal beliefs to intrude on the church's policy.