Even if it were taking place entirely on private property (which it isn't: their lines run across public land, and they are already giving up some rights to control that property due to that fact), they still must not interfere with the individual's right to contract. The exchange of information via IP is a voluntary exchange between two legal entities, and the exchange amounts to a contractual relationship (ie, the initial request is a unilateral contract). For an ISP to do any more than simply route that exchange is tortious interference of contract.
Even though the ISP might block the relationship before it exists (ie, preemptive network bias such as forging packets or simply dropping the initial request packets), it will still fit the terms. The contract is unilateral, so in the initiator's view the contract exists unless the receiving party fails to act of their own accord (letting the request time out, for example) or explicitly declines (sending a HTTP status code in the 400 range, for example).
Tortious interference, in the common law of tort, occurs when a person intentionally damages the plaintiff's contractual or other business relationships.