Votes in Parliament to relax abortion and same-sex marriage laws in Northern Ireland have made free speech "vulnerable", the Christian Institute has said.
It criticised the "rush job" to "force" gay marriage in the country, where such unions currently do not have legal recognition.
MPs in Westminster voted overwhelmingly on Tuesday night to extend abortion access and gay marriage to Northern Ireland if devolution is not restored by October 21. Stormont has been suspended since January 2017 due to a political deadlock.
The Christian Institute said that free speech would be "left largely unprotected" if the changes go ahead.
Director Colin Hart questioned why the vote had been taken with "no consultation and no consideration given on how to protect those who respectfully disagree with the redefinition of marriage to include same-sex relationships".
"When marriage was redefined in the rest of the United Kingdom, this was done so in the face of overwhelming public opposition," he said.
"But at least it was done following detailed consideration over many months. That time and public pressure ensured there were some free speech safeguards. What MPs have done this evening offers little or nothing in that respect.
"There is a whole host of legislation that needs to change. Free speech protections that have been won over many years must be put in place in Northern Ireland.
The Democratic Unionist Party has said that the votes by MPs breach the devolution settlement.
Sir Jeffrey Donaldson, the DUP's Lagan Valley MP, said the votes meant there was "very little incentive for Sinn Féin to restore devolution", the BBC reports.
"It's quite ironic for an Irish republican party to argue that the British Parliament is the proper place to deal with very sensitive legalisation, very sensitive matters," said Sir Jeffrey.
"[The DUP] believe the purpose of devolution is to allow the different parts of the UK to make laws that are appropriate for that part of the country."