Scottish churches fear losing charitable status and workplace discrimination if Holyrood legalises same-sex marriage.
The concerns are raised by more than 50 leading church figures attempting to lobby Holyrood as the Marriage and Civil Partnership (Scotland) Bill moves towards becoming law.
In a letter sent to the Scottish government, the group expresses "deep concern" over possible consequences of the Bill becoming law.
MSPs initially voted in support of introducing same-sex marriage legislation in November.
The Bill is entering a stage 3 debate tomorrow, where amendments will be proposed and discussed, before a final decision is made on its passage into law.
Church figures have called on Health Secretary Alex Neil, one of the Bill's principal drafters, to make certain amendments before it moves to the next stage.
In its current form, the Bill has protections for individual officiators who object to performing same-sex wedding ceremonies, and churches and other religious institutions will be invited to perform same-sex weddings on an opt-in basis.
But the letter's more than 50 signatories, who include ministers, pastors and congregational elders from across Scotland, argue that there is not enough protection for the charitable status of churches that decline to perform such ceremonies.
Without such a status, churches could lose out on many tax benefits, such as the ability to claim Gift Aid and certain VAT concessions, as well as being denied access to funds from charitable foundations.
"We are greatly concerned that following any change in the law some public bodies might refuse to enter into any partnerships or arrangements with a church which publicly states its opposition to same-sex marriage," the letter reads.
"We would therefore ask that the Scottish Government amends existing charity law so as to specify that holding or expressing the view that marriage is only between a man and a woman cannot be cited as a 'disbenefit' when administering the charity test.
"We would also support a clear principle of reasonable accommodation in ensuring churches and religious charities that are explicitly opposed to same-sex marriage can continue to openly provide services with public bodies, and to likewise make use of public facilities."
The letter's signatories also point out that there may be future issues regarding discrimination on the basis of opinion. They call for protections for individual employees who disagree with the law, even if their work does not explicitly involve the ceremonies.
"Will people working in the public sector who express the view that marriage can only ever be between a man and a woman be disciplined, or even have their suitability for employment questioned, on the basis that their views are deemed incompatible with their employer's commitment to equality and diversity?
"Likewise, will young Christians seeking employment in professions such as teaching or the police, find themselves at a disadvantage in the recruitment process should they express their opposition to same-sex marriage?"
The group calls on the Scottish Government to stand by a statement in a policy memorandum accompanying the same-sex marriage Bill, where the Scottish Government claims that it "respects the current view of marriage".
"We would urge the Government to have the courage of its convictions and to explicitly state on the face of the Bill that this view is indeed worthy of respect," they said.
"This would provide us with some reassurance that public sector workers who disagree with same-sex marriage will indeed have their view respected by their employers.
"We would also welcome a specific amendment to the Equality Act clarifying that compliance with the Public Sector Equality Duty (PSED) means ensuring no person suffers any detriment because they express their belief in marriage as currently defined".
The same sex marriage debate in Scotland has been controversial at some moments. In June 2013, Labour MSP Elaine Smith received multiple personal attacks on Twitter for rejecting the description of same-sex marriage as "equal marriage".
Speaking about the quality of the debate on this matter, Ms Smith said: "It is astonishing that a politician cannot represent the views of their constituents without being vilified and subjected to personal attacks.
"Speaking against the redefinition of marriage in modern Scotland, sadly, leads to verbal attacks which seem to be an attempt to try to shut down debate and intimidate opponents."
The Scottish LGBT advocacy organisation, Equality Network, has described tomorrow's vote as a positive milestone in Scottish history.
"Thirty-four years after Scotland decriminalised homosexuality in 1980, the Scottish Parliament will have the historic chance to remove this last major piece of sexual orientation discrimination from Scots law and secure legal equality for lesbian, gay and bisexual people," the network said.
The Church of Scotland's official position on same-sex marriage was first made clear in 2011, with a further clarification in 2012.
The Reverend Alan Hamilton, Convener of the Church of Scotland's Legal Questions Committee said that: "The Church of Scotland has already voiced opposition to same-sex marriage. Unless our General Assembly decides otherwise, we cannot support the Government's proposals on celebrating civil partnerships or same sex marriage."
In the same statement, Reverend Hamilton also affirmed the Church's support for all people regardless of sexuality: "We re-iterate that we believe homophobia to be sinful and we reaffirm our strong pastoral commitment to all people in Scotland, regardless of sexual orientation or beliefs."
