It's a voluntary system. The way the product regulations work is that you set limits on how many milligrams of mercury you can have in particular lamps and in other products. When an allowable limit of mercury is in a product, you, as a manufacturer or importer, have to put on the box that the product contains mercury, so that consumers know that when they are buying it. The next time you buy a light bulb you should look. You'll see that there's a little label on the box that says “contains mercury”. The instructions talk about being careful because mercury can cause problems, so you need to dispose of it carefully. I don't have the exact wording of the regulations off the top of my head, but that's essentially what they tackle.
On November 15th, 2016. See this statement in context.