Desertion was the crime of enlisted personnel abandoning the service in which they had been members.
Guri, Renth and Rellus Tagrim had all deserted the Takret Militia by 2152 because they considered their leaders to be corrupt. (ENT: "The Catwalk")
In 2370, Lieutenant Commander Calvin Hudson deserted Starfleet from his position as attaché to the colonies in the Demilitarized Zone to join the Maquis. (DS9: "The Maquis, Part I", "The Maquis, Part II")
Lieutenant Ro Laren also deserted Starfleet for the Maquis in the same year. (TNG: "Preemptive Strike")