An agreement among time-travelling powers of the far future that limited time travel to observation, which the factions of the Temporal Cold War ignored, and which was followed by an outright ban.
The Temporal Accords are first mentioned in the Enterprise episode Cold Front, in which the crewman Daniels tells Jonathan Archer that he comes from the 31st century and works to enforce them. By then time travel is common, and the accords allow it only for the study of history. Groups that reject them, such as the Suliban Cabal's unseen patron and the Na'kuhl led by Vosk, try to alter the past, and Daniels calls on Archer for help in Shockwave and Storm Front.
The struggle becomes open war. In the third season of Discovery, set in the 32nd century, Michael Burnham learns that after the Temporal Wars all time travel technology was destroyed and its use made illegal.
The ban is discussed again when the Guardian of Forever, in hiding since the wars, appears in Terra Firma, and when a leftover Krenim weapon traps Discovery in Face the Strange.