http://www.guardian.co.uk/society/2013/mar/29/amnesty-northern-ireland-gay-marriage

In 2005, two lesbians celebrated the first civil partnership in Britain.... in Belfast! Now the Stormont government bans gay marriage. A step backwards.... but not for long, we hope!

Interesting to see how the case turns out, as their apparent main argument (whether or not they can "found a family") is invalid as they already can as Civil Partners.

... and there's certainly no "international law" that says that different parts of the UK can't have different laws on marriage, discrimination, or anything else - Northern Ireland / England and Wales / Northern Ireland have three totally different legal systems and three different (but overlapping) legislatures.