Labour and the Lib Dems in Scotland have both vowed to change the law to allow homosexual civil partnerships to be registered in churches, mosques or synagogues.
The two parties made the commitments in their manifestos ahead of Scottish Parliamentary elections on 5 May.
There is no such commitment in the manifesto of the Scottish Conservatives, and the Scottish National Party has yet to launch its manifesto.
The issue is entirely separate from that of legalising full same-sex marriage, which the Lib Dems also support and which Labour has promised to consult on.
In Scotland at present, homosexual civil partnership registrations are civil arrangements and by law they cannot take place inside religious buildings.
Last year the Westminster Parliament changed the law for England and Wales to allow churches, if they wish to, to perform such registrations on their premises.
The change has yet to come into force. The Government in London is currently consulting on how the new law will work in practice.
Although the new law for England and Wales does not force churches to take part, critics say it may become coercive in the future.
Earlier this year, a number of evangelical organisations including The Christian Institute issued a joint statement voicing their concern about the issue.
The statement noted that a small number of religious groups already allow their clergy to bless civil partnerships, but added that these groups are also keen to be able to register the controversial unions.
The statement said: “In response to the demands of these groups, the Government is embarking on a course of action that is bringing it into conflict with thousands of evangelical churches and the Church of England and the Roman Catholic Church.”
The organisations also warned that changing the law to allow civil partnerships in churches would breach previous assurances made to Parliament about the nature of the same-sex partnerships.
The statement said: “It is a breach of undertakings made by Government ministers during debates on the Civil Partnership Bill.
“Parliament was persuaded to pass that Bill, in part, because it was made clear that civil partnership was a civil rather than a religious institution and would not take place in religious premises.”
The evangelical bodies also warned that any new legislation must protect churches that disagree with the same-sex unions from litigation.
The Government has previously suggested an ‘opt-in’ scheme for religious bodies that want to register civil partnerships, which it says will protect churches.
The evangelical groups’ statement concluded: “When it comes to equality legislation, permission often turns rapidly into coercion.
“In a country where faith-based adoption agencies have been forced to close or cut their religious ties by equality law, where Christian marriage registrars can be dismissed for their religious views on marriage and where Christian B & B owners are forced to pay compensation to same-sex couples, Christians will need a great deal of reassurance that the Government is not about to do something that will make their situation even worse.”
The joint statement, entitled Homosexual marriage and the registration of civil partnerships in churches, was signed by five evangelical Christian organisations.
These were Affinity, The Christian Institute, Christian Concern, Reform and the Fellowship of Independent Evangelical Churches.