The long-form census is the census, so it's mandatory as it's written now.
This long-form census ceased to exist in 2011. It was replaced by something very different, but the whole thing, the short and long forms, are the census. Now we may have another model. In the U.S. they have a short census, and they have a rolling sample inquiry that goes out on a regular basis with a long set of questions, like a long-form census. It's a sample of the population, but there's still an obligation.