Temporal Prime Directive

The Temporal Prime Directive is a Federation Starfleet principle that members of Starfleet should avoid directly interfering with the timeline in instances of time travel. 

In 2374, Q referenced the Temporal Prime Directive as why he could not explain to Jonathan Masters the meaning behind his statement that it was not yet time for Masters to die. Q stated that the directive meant that Masters should not ask such a question of a person who knew about future events since it could lead to an altering of the timeline.