Tail docking is the removal of a dog's tail, usually painfully done between 10 and 14 weeks of age without the use of anesthetic. It is an abusive practice.
Tail docking is illegal in 41 countries. Others have tight restrictions on the practice.
Dogs need tails for communication. Tails communicate fear, aggresion, caution, playfulness and more both to other dogs and to people. Tails are rudders when swimming and aid balance.
The Canadian Situation: Veterinary Professional Associations ban docking by Vets in New Brunswick and Nova Scotial. However it is not law and breeders often do their own docking. There one restrictions in other provinces.