Slamming is the practice of switching one company's customers to another company providing the same service without the consent, and often without the knowledge, of the actual customer. When a customer is slammed to a new company, they may find themselves facing charges and conditions they never agreed to, and are often required to pay those charges to avoid disconnection of service. These charges can usually be recovered through legal action, but the cost and inconvenience of legal action has often forced customers to swallow the costs.

Energy industry deregulation laws in the US normally prohibit the practice of slamming and prescribe penalties for companies caught in the act. Slamming was a relatively common practice in the telecommunications industry in the 1990s until legislators clamped down on the practice.

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