The High Court will give a decision tomorrow in the case of a lesbian couple seeking legal recognition for their relationship.
Ms Ann Louise Gilligan and Ms Catherine Zappone are seeking a judicial review of the refusal by the Revenue Commissioners to recognise them as a married couple for tax purposes.
The women were married in Canada in September and hold a Canadian marriage certificate, the court was told today.
Dr Gerard Hogan SC, representing the women, contended that if a man and woman had presented a similar marriage certificate to the Revenue Commissioners, it would be accepted.
Dr Hogan said that neither the taxes act nor the Constitution contained a definition of a married couple.
Even if the "original intention of the Oireachtas when drawing up the Constitution was to construe marriage as different-sex couples then that is now, a - unconstitutional, or b - incompatible with the European Convention," he argued.
Dr Hogan said "the women had been discriminated against in an unjust manner, in breach of their Constitutional rights".
Mr Justice McKechnie will give his ruling tomorrow morning.
If successful, the case would have wide-ranging implications for all cohabiting couples. According to the last census, taken in 2002, there were 77,600 family units based on cohabiting couples in Ireland, a figure that had more than doubled since the previous census. Two-thirds of them were childless.
In the same census 1,300 couples described themselves as same-sex cohabiting couples - of whom two-thirds were male. It is thought that many cohabiting same-sex couples do not identify themselves as such in the census.
