Protections for charities, churches and public sector workers must be included when same-sex marriage is introduced in Northern Ireland, The Christian Institute has said.
The call is supported by pro-LGBT groups Amnesty International and the Rainbow Project.
Same-sex marriage is to be imposed on the Province following a vote by Westminster MPs in July.
When same-sex marriage was introduced in other parts of the UK, protections were put in place to allow for conscientious objections.
But the Northern Ireland Office, which has pledged to consult on the change, has so far declined to say whether it will consider similar protections for the Province.
It has simply said it is working to put legislation in place by 13 January 2020 to introduce same-sex marriage and opposite-sex civil partnership.
Simon Calvert, a Deputy Director at The Christian Institute, said: “When marriage was redefined for England and Wales, the legislation contained strong protections for free speech and religious liberty.
“There were lots of debates about it and lots of promises and pledges from the government and supporters of same-sex marriage, that the rights of people that disagree with same-sex marriage would be protected.
“However, there wasn’t any of that when the NI Executive formation legislation was going through.”
The Institute is calling for protections for public sector workers, school children, churches, religious charities and the upholding of free speech.
Rainbow Project Director John O’Doherty agreed. “We, as with the position of the Christian Institute, believe that the protections in place in England and Wales should be extended to NI”, he said.
Patrick Corrigan of Amnesty International said: “We want the same protections and freedoms available in England and Wales to be available in NI.”
At the same time as MPs voted on marriage, they also backed imposing abortion on Northern Ireland.
The Government is currently consulting on introducing an abortion law that would go far beyond the rest of the UK – with no reason needed for an abortion up to 12 or 14 weeks.