You think things are better there?
Overtime can be a messy area. It's probably up to your manager to make she he/she has any overtime authorised by senior management before agreeing it with workers. Just because your manager says you can come in, doesn't mean it'll be paid. It ought to, but it doesn't, because the whole idea is to put pressure on the managers to deliver more for less.
This kind of thing is only going to get worse. Sales across the big supermarkets are up, but that's because of food inflation double the official rate, not real increases in sales & profits. Our store just received a payroll cut because although sales are up, volume's down. Oh joy!
Hang onto your hats folk, this recession has only just begun! :-/
Andrew McP
PS Being in a union is, in theory, a good idea. I'm not, but that's because I got sick of handing over a tenner a month only to watch them roll over and play dead. But to be fair, employment rights these days are so strong (in general) that Unions are far less important. In fact if you ask me -- and I speak as shop floor pleb, not a manager -- the pendulum's swung too far in the employee's favour. Sacking lazy baskets has become a nightmare, making it harder for employees with a conscience get any kind of job satisfaction. Assuming such a thing exists in a big retail chain.
PPS In the first job I ever had, at a filling station over 30 years ago, one of the mechanics said to me not long after I got there... "Repeat after me... I must work harder, for less money! That's the only thing you'll ever hear throughout your working life." And he was absolutely right.