The Venka Treaty was a legal document which was signed by the United Federation of Planets and the So'ja Republic in 2377. (Star Trek: Pioneer)
The treaty gave the Federation permission to send a Starfleet vessel into So'jan space in the purpose of exploring and examining the many inherent properties, both scientific and power-based, found within the Venka Nebula's gaseous particles. However, the treaty fell apart in 2378, when the So'ja Rebellion attacked the Federation science vessel, the USS Clark, which had been sent into the nebula to begin the research permissible in accordance with the treaty. ("The So'ja Incident")
In 2381, the So'ja Coalition reopened the Venka Nebula to the Federation for scientific research into the nebula's energy potential. Ensign Eric Zimmer, of the USS Pioneer was allowed to pilot a shuttle-craft into the nebula to take readings. While within the nebula the shuttle was attacked by a So'ja vessel, which was subsequently destroyed when Ensign Zimmer returned fire. Unfortunately, there was no evidence indicating that the So'ja vessel had attacked the Federation shuttle, leaving Zimmer accused of causing an interstellar incident. However, other than a formal reprimand and some time in the brig, Starfleet Command and the Federation Council agreed not being Ensign Zimmer up on charges. ("Complications")
Later in 2381, during the interrogation of the So'ja operatives, whom attempted to assassinate Federation President Korvin Mot, the truth about the incident involving Ensign Eric Zimmer was revealed. The assassin admitted that the So'ja vessel did fire first, and also to the fact that they had a plant within Starfleet who manipulated Ensign Zimmer's shuttle's records to implicate the the ensign in wrong doing. ("In Custody")