Two members of the board - George Oldham and Sarah Lupton - are facing one another in the battle to be vice-chair.
The pair argue for two very different futures for the organisation, Oldham being a member of the ARB Reform Group and Lupton being independent.
Whoever wins the race will act as deputy for the chair Humphrey Lloyd, who has guided most of the ARB's most controversial policies over the last two years.
It is an important role, and if Lupton were to win it would result in the ARB Reform Group being sidelined, despite winning an overwhelming mandate at the recent board elections.
The group won five of the seven seats on the board set aside for practising architects and picked up 70 per cent of the vote.
They campaigned as a loose coalition that believed the activities of the ARB should be pared back to a bare minimum.
The vote for the new vice-chair will be among all the board members, taking in the seven practitioners and eight lay-members.
A result is expected on 11 May.