The company is wrong to tell you that you have to work 30 days after December. As you started in September then after you had 30 working days, not counting any classroom time. All classroom time is in addition to the 30 working days and the company may add up to 10 classroom days for a total of 40 days. If you started September 1, 2005, as long as you worked 30 days by January 1, 2006 then you should have reached seniority. The 120 days is a rolling time frame. Sounds like you need to get the union involved right away. You only have 90 days to argue any discrepencies involving seniority or pay issues.