Priority one
From Memory Alpha, the free Star Trek reference.
Priority one is a type of communiqué used within the Federation that noted messages of high priority.
In 2269, Uhura sent a priority one call to Governor Robert Wesley of the planet Mantilles to warn him of the danger of an approaching cosmic cloud. (TAS: "One of Our Planets Is Missing")
In 2285, Captain J.T. Esteban instructed his communications officer to send a coded priority one message for Starfleet Commander. In his message he stated: "Federation science vessel Grissom arriving Genesis planet to begin research. J.T. Esteban, commanding." (Star Trek III: The Search for Spock)
Prime Minister Nayrok sent the Enterprise-D a priority one message on a priority channel, after Roga Danar escaped from the ship and captured an Angosian police shuttle. (TNG: "The Hunted")
In 2366, Captain Jean-Luc Picard received a priority one message on a secured channel from Admiral Haden concerning the Romulan defector Alidar Jarok. (TNG: "The Defector")
The following year, Data sent a priority one message to Worf ordering him to arrest the brainwashed Geordi La Forge in order to prevent him from assassinating Governor Vagh. (TNG: "The Mind's Eye")
Admiral Nakamura sent a priority one message to Captain Picard in 2370. Worf was ordered by Picard to sent the message to Doctor Crusher's office in sickbay. Nakamura informed Picard that he initiated a fleet wide yellow alert, because Starfleet Intelligence has picked up some alarming reports from the Romulan Star Empire. (TNG: "All Good Things...")
In 2372 Lieutenant Commander Jadzia Dax received a priority one message from Starfleet Intelligence which stated that the Klingons placed Orbital defense systems in Cardassian territory. (DS9: "The Way of the Warrior")
