In the bookshop in which I volunteer, there are two paid employees - the FT manager and PT deputy manager. (It's a charity shop.)
I've been aware for a while that the charity does not pay the shop's employees for any overtime they do (which is probably the main reason that the deputy manager generally refuses to work more than her contracted hours.) But I assumed that since this was the case, they could therefore not expect employees to do overtime, since it's not paid.
However, the manager is under pressure to keep the shop open for longer during the week and to also keep the shop open on Sundays when the volunteer team for that day are unable to come in. Sunday is the one day when there is no paid member of staff in the shop and it's entirely volunteer led, but but occasionally there are times when the volunteers can't come in to do their shift and when that happens the shop is closed on that Sunday.
From a recent conversation I had with the manager, it seems that the charity does indeed expect her to do unpaid overtime, and there is so much pressure that it seems she is more or less almost forced into doing it.
Discussing this with other volunteers, I learned that the charity offers time off in lieu for unpaid overtime, and that it would be in the employment contract. Time off in lieu would be reasonable IF taking additional time off was usually a practical possibility, but given the nature of charity shops relying on a staff of majority volunteers, taking additional time off is often NOT a practical possibility.
So what seems to happen in practice is that the manager ends up doing overtime that is completely unrenumerated in any way.
This set-up seems unfair to me. In typical retail, I imagine time-off in lieu of payment for overtime would be more reasonable, because all the staff contractually have to be there, so there're more flexibility and consistent cover. This is not the case with charity shops.
Given the nature of charity shops, I think that the charity should either commit to paying any overtime they demand - or at the very least, they should not put pressure on their employees to do the overtime when they're aware that it can't really be compensated.