I used to dread the envelope coming round in my twenties as I was so desperately skint, I was secretly stealing milk and toilet rolls from work. The pressure was huge - two people standing over you in front of everybody else, glaring and then writing 'To Pay - MOONCUP' on the envelope if I didn't have a fiver on me and in one case telling me not to bother if it wasn't a note as I pulled the handful of change out that was actually all I had for the next three days.
Fortunately, that display of arseholeness gave me the final push to say 'Well, OK, then, I won't fucking bother'.
Since I got older/discovered my spine, I'm now in a position where I will publicly say I think it's wrong to put pressure on people because nobody knows other's personal circumstances. I've also refused to contribute to a refreshments fund that was painted as compulsory - no, I am not paying for other people's milk, sugar, snacks and pizzas when they never, ever try to cater for any dietary, religious or health needs.
My current work has a scheme where you can choose to donate once a year and it's kept completely confidential - you're not approached personally, nobody puts further pressure on you, if they're running low on funds, they email a generic 'would anybody who hasn't contributed consider making one if they are able' to everybody so there's no identifying who has chipped in and it's the most responsible and unintrusive way of doing it.