Hi, I'm a part time package handler at my hub. When I signed up for the job I agreed to work the 2nd half shift which is 440am - 9am or 10am. Recently the last few weeks management has been telling us on our day 6 which is Friday night that all part time handlers are required to work day 1 (Sunday) or they initialize a new start time for us on day 2 usually from 10pm-1150pm depending on business needs. I have been repeativly reminded supervisors that I cannot work these hours as a part time employee as I have other life commitments. So today I go in at my normal schedule time at 440am, and was instructed to go to the office where I also met with two other part timers. The supervisor asked why we weren't here when scheduled (1130pm) and has threated us with disciplinary action if we do not show up tonight at 1150pm. I find this unfair and have spoke to other employees that believe it is wrong to punish us for having other responsibilities besides working when UPS wants us to work. We should not be treated as if we are disposable. Is this grounds for filing a grievance? My plan is to show up when I'm regularly scheduled at 440am knowing I'll be getting sent to the office. Should I make it clear I will be filing against said supervisor right then and there or?