Since I have not read your CBA I cannot tell you what rights you have through the union. I can only tell you what the law says. You will have to discuss any additional rights the union contract may give you, with your steward.
The situation you describe was almost certainly legal. However, there is one small question in my mind that might or might not help you. To know for certain if it will, I need you to answer the following questions:
1.) How long have you worked for this employer?
2.) How many employees does the employer have within 75 miles of your location? (If exact number not available, is it over or under 50?)
3.) In the last 12 months, did you work a minimum of 1,250 hours?
4.) In the last 12 months, how much sick time have you taken?
5.) What state are you in?