Lisburn City Council faces legal action if it does not overturn a ban on the use of its wedding room for same-sex civil partnership registrations.
Germany introduced similar equality legislation in 2001
The Gay Rights Association said it was "blatant discrimination" and plan to mount a court challenge to reverse it.
A law allowing same-sex couples to enter into a civil partnership comes into effect in December.
Lisburn councillors encountered protesters as they arrived for their monthly meeting on Wednesday night.
A motion proposing that same-sex civil partnership registration should "be not afforded the same recognition" as a civil marriage ceremony was tabled by Alliance councillor Seamus Close and passed in July.
It also proposed that the council's wedding room, the Cherry Room, should not be used for such registrations.
Patricia Lewsley from the SDLP said it amounted to discrimination, an accusation echoed by Sinn Fein's Paul Butler.
But Ulster Unionist councillors said they were legally entitled to withhold the use of the room.
Robert Toner from the Gay Rights Association said it was discrimination against the gay and lesbian community in Lisburn.
"A male and a male getting married is a gay marriage and a lesbian and a lesbian getting married is a gay marriage.
"Equality in Lisburn? It's totally wrong, it's discrimination, the council needs to admit to that.
"I will be taking a case against Lisburn on discrimination. I'm confident I will win this case and make Lisburn a city for all."
However, Mr Close said the council had made a distinction with civil partnership and civil marriage ceremonies.
"I want to clearly demonstrate that there is a distinction between a civil marriage, which is a union between a man and a woman, and a civil partnership which may be lots of things but is not the latter," he said.
"The distinction between a civil partnership and a marriage is not being made by Seamus Close, it is a fact of life.
"There is this confusion and there are those who would appear to me, and to others, who want to build on this confusion. You cannot have a gay marriage."
The Civil Partnership Act creates a new legal relationship, which two people of the same-sex can form by signing a document.
It provides same-sex couples with parity of treatment in a wide range of legal matters with those opposite-sex couples who enter into a civil marriage.