What generally prohibits a claim from being part of the supplemental jurisdiction?

The correct understanding lies in the nature of supplemental jurisdiction, which allows federal courts to hear additional claims that are closely related to ones within their original jurisdiction. A claim that introduces new plaintiffs typically does not qualify for supplemental jurisdiction under 28 U.S.C. § 1367 because it can create complications regarding the original jurisdiction of the court. The presence of new parties can alter the case fundamentally and affect the diversity or federal question jurisdiction, ultimately leading to a situation where the federal court lacks jurisdiction over those claims involving new plaintiffs.

A claim based solely on state law can still be heard under supplemental jurisdiction as long as it meets the requirements of being related to the original claim. The unrelated nature of a claim to the original claim (the option referring to unrelated claims) is also a crucial factor: if a claim does not arise from the same transaction or occurrence as the original claim, it typically cannot be included under supplemental jurisdiction. Lastly, concerns regarding parties from the same state do not inherently preclude claims from being part of supplemental jurisdiction but may trigger issues with diversity jurisdiction specifically.

Thus, the introduction of new plaintiffs fundamentally alters the scope of what can be heard under the principles governing supplemental jurisdiction.