poach on (one's) territory

To encroach on an area of land or part of a market that one currently controls or has jurisdiction over. The telecom giant has launched a legal campaign against the new service in an effort to prevent it from poaching on its territory. The indigenous tribe was awarded a huge reparation payment after a federal court agreed that the government had unlawfully poached on their territory for hundreds of years.

poach on someone's territory

encroach on someone else's rights.