Temporal displacement policy
The temporal displacement policy was a series of guidelines instituted by Starfleet which obligated its officers to take no action which could alter the course of history if they were to travel through time.

After having accidentally traveled back in time from 2371 to 2024, Julian Bashir expressed his dissatisfaction with the temporal displacement policy when informed by Commander Sisko that they could do nothing to help the hundreds of people who would be killed in the Bell Riots, which would occur in only three days time. ()

See also 
Temporal Prime Directive

Appendices

Background information 
This policy would later inspire the writers to create the Department of Temporal Investigations in . ()

Apocrypha 
In the non-canon  , the policy also specified that if a starship from the past were to encounter a starship from the future they should maintain communications silence and reduce the viewscreen's resolution to its lowest point, unless the future starship hailed them. This particular note was contradicted in . It also stated that if the ship from the past was facing a situation in which it was not likely that it could be saved, then the starship from the future could take the crew of the past starship on board. This is consistent with the reaction of the alternate  crew in , as the temporally displaced  was initially invited to rejoin Starfleet in 2366 rather than returning back through time to their near-certain demise. It was not until additional information came to light that the extraordinary decision was made to send them back anyway, despite the overwhelming likelihood of destruction.

External link
 
Time travel
Legal documents