Part of the issue with the optional working Sundays is that it is only since the late 1990s that the rail service on Sundays has grown, yet instead of addressing the right to refuse work this day, the industry has attempted to rely on overtime. Even in the late 1990s the majority of suburban services in the West of Scotland didn’t run. Places like Barrhead, Kilmarnock, East Kilbride, Milngavie, Cumbernauld, Croy and Neilston had no service whatsoever.
Whilst society has moved on in that time, rail staff have maintained quite a strong position and have been able to retain their right not to work that day. This is why it is such a hot potato as many will not want to lose this right, no matter how much you offered them.