The DUP's attempt to introduce a conscience clause Bill looks set to be defeated after Sinn Fein teamed up with the Green Party and NI21 to block it.
Sinn Fein's Caitriona Ruane said her party would use a petition of concern to stop the Private Member's Bill in its tracks when it comes before the Assembly.
It's being introduced by the DUP MLA Paul Givan after the Equality Commission said it would take legal action against Ashers Bakery following its refusal to bake a cake with a pro-gay marriage message iced on top.
The commission took the case on behalf of the gay man who requested the cake, claiming the family-run bakery had been in breach of legislation preventing discrimination.
The DUP has said its move would allow those with strongly-held religious beliefs to legally refuse to provide goods and services which contravened those beliefs.
But the Bill looks set to be blocked by the petition of concern - effectively an Assembly veto that requires the the support of 30 MLAs. Sinn Fein has 28 MLAs, but with support from Green Party MLA Steven Agnew and Basil McCrea of NI21 it has reached the number required.
The SDLP's Alex Attwood said if the Bill was ever tabled, his party would also sign the petition of concern.
Mr Givan claimed Sinn Fein was not prepared to even have the matter debated in Stormont, and there was nothing to even petition against at the moment.
"What they are seeking to do is shut down the debate my consultation document has started on how freedom of conscience might be protected through reasonable accommodation. Sinn Fein, along with their helpers, are not blocking legislation but seeking to stifle debate," he said.
"By preventing the Assembly even discussing the issue or allowing a committee to examine it, you are indicating that you simply don't care about how people with deeply-held religious beliefs are treated."
Ms Ruane said later: "We have lobbied other MLAs in the Assembly to back a petition of concern to block what in our view is an attempt to bring in discriminatory legislation. I have called on the SDLP and Alliance parties to support us but am now confident that we can reach the threshold to block this Bill from becoming law.
"It's important, therefore, that we as a society send out a clear signal that the days of banning certain sections of society from shops or services are long gone."
Mr Agnew yesterday confirmed that he had signed the petition.
"The so-called 'conscience clause' is nothing but a thinly veiled attempt to legalise discrimination against LGB people," he said.
A public consultation on the bill closes on February 27.
Story so far
The so-called conscience clause was introduced by Paul Givan MLA as a Private Member's Bill in December 2014 in response to the furore over the 'gay cake' row.
The owners of Belfast baker Ashers have been taken to court by the Equality Commission of Northern Ireland for its refusal to supply a cake to a gay man with slogan that supported gay marriage rights.