Politicians clashed today at the Assembly over attempts by Ulster Unionists to hand Sinn Fein's Martin McGuinness the title of First Minister.
UUP Assembly members were reprimanded by Speaker Willie Hay after they used the title in an attempt to highlight that Mr McGuinness and Peter Robinson share equal power in a joint office.
But Mr Robinson also became involved in the spat and complained that Ulster Unionist David McClarty, who acts as deputy speaker at the Assembly, was among those who failed to stick to Mr McGuinness's title of Deputy First Minister.
The row emerged as Mr McGuinness took questions from Assembly members on last month's meeting of the North-South Ministerial Council, but when Mr McClarty referred to him as Joint First Minister and then simply as First Minister the Speaker intervened.
Later the DUP's Jim Shannon said: "Mr Speaker when it comes to addressing the deputy First Minister, can the Speaker make a ruling in relation to some of the terminology that has been used today.
Gesturing towards his own DUP benches, he added: "He has been referred to as Joint First Minister, as First Minister and quite clearly the position is Deputy First Minister, as the First Minister is over here."
Mr Hay said: "Let's not play games in this House... We have a First Minister and a Deputy First Minister."
The titles of First Minister and Deputy First Minister were first introduced under the terms of the Good Friday Agreement.
Since the DUP took the top office, Ulster Unionists have said that use of the term deputy may give the public the impression the two most senior ministers do not share a joint office.
First Minister Peter Robinson intervened in today's dispute, hitting out at Lagan Valley Ulster Unionist Basil McCrea for first confusing the titles.
Mr Robinson added: "But it was then later made by a deputy speaker and that is a most serious issue."
The Speaker said he had been clear in his guidance to the Assembly and warned members against challenging the authority of the chair.
Mr McGuinness made no comment during the exchanges.