The problem is that when a full time vacancy arises there should be a meeting between the DOM and Local Rep under the filling of vacancies agreement sometimes known as the Stoke Agreement.
It takes about 12 weeks to recruit to a vacancy so there is ample time if the local Rep cannot agree to go through the disagreement procedure.
The first thing which should be discussed is are there current part timers working above their contracted hours on the same duty every day ?
If so there would be an argument that this individual should be given an increased contract and maybe the resultant vacancy filled by recruiting a part timer.
In line with the Way Forward the most senior part timer not necessary the part timer who has actually been working the additional hours.
The discussion in line with the Stoke agreement are based on workload and in principle is there enough inward work ? Sadly due to automation , improvements in Address Interpretation and Tops 2000 and the buddying system the indoor work is reducing.
The counter agruement is sick leave has increased. Attendance calls , parcels , door step scan , tracked etc has increased and time outside is often longer.
In terms of overtime bans or work your hours , the reality is what happens when the manager takes you off of pay which they have done before. You end out unofficially and whilst there is a time for that ! The best way is as Fish says ballot for strike action.
Next year there will be a national ballot on a whole host of issues ranging from pensions to later starts to data capture etc.