At my hub the sups first asked (more like begged/pleaded) seasonal temps to work extra shifts because seasonals during free-time only make OT after 40 hours per week, or aveage 8 hrs/day; management could get nearly 2 full shifts per day from the temps and only pay straight-time, saving thousands per day on OT on a few hundred workers per shift.
The seniority workers made OT after only 5 hours per day (25 hours per week). So they were asked last, [sarcasm]and you had to have really good hearing to hear the sups asking (mumbling) from across the hub with all the machinery going[/sarcasm]...so the seniority had to force the issue with management and flex their rights if they wanted extra hours.