Yeah.. In our department we tell new hires, "You need to look out for yourself for your breaks. You get 1 break if you work under 6 hours, you get two breaks if you work 6 hours or over. It's up to you to remember to take them and time them with others."
If it's time for you to take a break, tell a supervisor and take one. If they ask you to wait or tell you it isnt time, ask them when you can go. When that time comes, then go. Tell them, "The union guarantees I get a 15 minute break. If I don't get it I will file a grievance." Then follow through on your words.