Posted elsewhere: Five years at a job, listed as 35 hours a week, but never worked less than 40. Am I getting cheated?

I recently asked payroll about a floating holiday discrepancy and was told that the difference was due to my being a 35 hour a week employee rather than a 40 hour a week one. I've never worked less than 40 per week, usually 42 or more, and I've been here five years. I'm paid hourly, so they aren't shorting my hours; I'm just wondering why I would be listed as a 35-hour a week employee when I have never worked so little. I've called my union representative already and left a message. What should I expect to talk about when I hear back from him?