Under the current six strikes model, which most major ISPs participate in, a user is sent increasingly annoying warnings each time an instance of copyright infringement is detected. After five or six warnings, the ISP is authorized to slow the connection for a period of time, or even shut it off temporarily. This has proven to be a fairly weak deterrent by Comcast’s own measures. Going too far the other way comes with its own problems.
A number of European countries have instituted three strikes laws that carry harsh penalties for people suspected of repeated infringement. France was an enthusiastic supporter of its version of three-strikes called Hadopi. Under this system, a user would receive two warnings, then after a third alleged incident, their internet access would be cut off.