Peers opposed to the registration of civil partnerships in religious premises have secured a debate in the House of Lords that could see the provision scrapped altogether, after warnings that churches could face litigation for turning away gay couples.

This month the equalities minister, Lynne Featherstone, said the government was committed to removing the legal barrier to civil partnerships' registration on the religious premises "of those faith groups who choose to allow this to happen", adding it would be a "permissive measure" with "no obligation on faith groups to host civil partnerships". The change to the equality bill, known as the Alli amendment, was passed in March 2010.

But peers, led by Lady O'Cathain, will debate the change on 15 December – 10 days after it comes into effect – in an attempt to scupper it entirely amid continued fears that churches will be under pressure to opt in to the voluntary scheme. If successful it would prevent all religious premises from registering civil partnerships – including those happy to do so.

Mark Hill QC, an ecclesiastical lawyer, in a submission to the House of Lords merits of statutory instruments committee, criticised the Alli amendment, calling it "somewhat unsatisfactory". "It presents a profound difficulty for a significant number of faith groups who regard same-sex relations as inimical to their sincere beliefs, yet (probably more through oversight than design) it only partially satisfies the secularists (and those faith groups for who same-sex relationships are compatible with their beliefs), allowing a religious building to be used for what remains a wholly secular function."

Current legislation allows for certain religious organisations to lawfully discriminate against sexual orientation, thereby preventing civil partnership registrations taking place on their premises.

But Hill said local authorities were charged with eliminating discrimination on the grounds of sexual orientation and argued a local authority could "legitimately be constrained by this public sector equality duty from registering places for the solemnisation of marriage unless and until the proprietors of that place had sought and obtained approval for the registration of civil partnership".

He added: "It is a curtailment of religious freedom in that it will compel faith groups either to cease their registration of buildings for the solemnisation of marriage and therefore their ability to celebrate a sacred liturgical wedding which has civil effect; or it will compel them to secure approval for the registration of civil partnerships despite their doctrinal objection to same-sex relations.

"In consequence, faith groups are placed in the invidious position of being dependent upon the discretion of each and every local authority, whose decisions in any event will be reviewable in the administrative court at the behest of any lobbyist."

His concerns are shared by the Christian Institute, Care and the Evangelical Alliance. Derek McAuley, the chief officer of the General Assembly of Unitarian and Free Christian Churches, said the move appeared to be a "cynical effort to derail the measure on rather spurious grounds".

"The amendment to the equality bill permitting registration originated in the House of Lords and was passed with wide support. We are confident the legislation offers the protection to those churches who hold a differing view on this issue and do not wish to register their premises for this purpose. They have that freedom.

"Unitarian congregations must not be prevented at this late stage in seeking to take forward our own sincerely held views and to offer same sex couples the opportunity to register their civil partnership".

Progressive Jewish movements and Quakers are some of the groups willing to host civil registration ceremonies. But the Church of England and the Roman Catholic church have insisted that neither their buildings nor their clergy will be involved.