Upon taking their seats members of the Northern Ireland Assembly are required to designate themselves as either "unionist", "nationalist" or "other". MLAs are free to designate themselves as they see fit, the only requirement being that no member may change his or her designation more than once during an Assembly session.
A vote will not automatically require cross-community support. A "Petition of Concern" must first be presented to the Speaker by at least 30 of the 90 members (108 members before 2017). In a cross-community vote the majority of unionists and the majority of nationalist votes are required to pass a motion put to the Assembly.
This was originally set out in the Northern Ireland Act 1998.