If you want to stop people working days off then why not do it properly and organise a ballot through BALPA for members of both Scotia and Bristows.
If you can get both sides to stop doing it then there will be less pilots available to take up the slack. It's also worth remembering that even if some pilots continue to work days off at the current flying levels they will only be able to do it on a few occasions before they start to bust flying and duty hours/days off regulations. Thats when it'll start to work and hell if you feel that strongly about it keep an eye on those pilots who work days off and if they bust their limits report them to the CAA.
Remember there is a flight safety issue here and some North Sea pilots are feeling the stress of the extra workload without working days off. It's not that long ago when a pilot was sacked for falling asleep on the North Sea because he had been working late the night before on another job.