Well, if you were doing the same (2) jobs for the same (2) shifts for the last 5 years, and now you've been told to report to different shifts, I'd say you are laid off (one or both of your jobs/shifts is eliminated). Your local should make sure this is being done properly, meaning: no part-time employees still doing the same work you did on each of your shifts. If that is the case, your steward/union rep./BA would be the best one to explain what your options are: bumping less senior 22.3, double or split shifting two part time shifts, working one PT shift only, or taking the layoff and applying for unemployment compensation. Until the grievance is resolved, you may have to report to work as directed, unless this change in shift times creates some hardship that might afford you some other form of relief (like being the primary caregiver for a sick child/take FMLA time).