There are many types of veto in Avalon, from the Council of Lore electing to veto specialisations or proposed Head of the Loremaster Profession, to the Cardinal's veto on decisions of the Second and Third Estate. Each are dealt with in their own secions, e..g. HELP LORECOUNCIL and HELP CARDINAL.
The Order of Veto is, along with the oath of allegiance, the key power of the council of Barons (generally elected by universal active citizen suffrage).
The oath of allegiance decides a city's Prince or Prince and must be unanimous across all Barons. With the oath-mandate the Prince becomes the most powerful of citizens with the honour of representing the Crown: deciding on ministers or, by delegation, bestowing the Prime Ministership and - in broader terms - remaining the ultimate authority and defining influence in a city or town's historical decisions.
The Order of Veto is a more contentious affair and only comes into play under extraordinary circumstances. It represents a fundamental schism twixt Baron and Prince in the choice of Prime Minister and since the Prime Minister inherits most of the practical powers of the Prince and the various ministers (including ministerial selection), an Order of Veto is a serious matter. If a majority of Barons declare an Order of Veto against a Prime Minister, the Prime Minister automatically loses ALL of his/her powers and privileges until the disagreement is resolved. If there is a unanimous spread of Order of Veto declarations by all members of the baronial council then the very decision of the Prince is overturned and the Crown is forced to strip the Prime Minister of his/her rank, powers and privileges; permanently.
To issue an Order of Veto the Baron must type VETO followed by the name of the Prime Minister. This is a public, city-wide and ACTION-recorded declaration. In a council of five, a single Order of Veto will not depose a Prime Minister but - depending on certain constitutional points - two and certainly three of the five issuing an Order of Veto will disempower the Prime Minister completely.
To reverse an Order of Veto, the Baron types UNVETO followed by the name of the Prime Minister. This, like the VETO, is a public, city-wide and ACTION-recorded declaration. If the reversal of an Order brings the number of active vetoes below the majority, the Prime Minister regains his/her powers and privileges.
New Barons begin with presumed support for the Prince's chosen Prime Minister and a new Prime Ministerial choice presented by the Prince/Princess to the monarch will automatically reset any outstanding Orders of Veto to neutral/support. Notifications are posted to Barons in MSG form if they are not in the land at the time of presentation; as are Orders of Veto to the Prime Minister if affecting his/her powers and status.