- You may also be looking for the Second Khitomer Accords which outlawed subspace weapons.
The Khitomer Accords refers to two historic treaties signed between the United Federation of Planets and the Klingon Empire. The Accords receive their name for the Klingon colony of Khitomer where the first peace treaty was signed at the Khitomer Conference in 2293. (TOS movie: Star Trek VI: The Undiscovered Country; DS9 episode: "The Way of the Warrior"; ST reference: Federation: The First 150 Years)
In 2370, retired Starfleet Captain Montgomery Scott devised a plan to take a B'rel-class Klingon bird-of-prey, the Bounty 2, back in time and rescue his former commanding officer, James T. Kirk, Scott had the forethought to utilize the shuttlecraft Goddard rather than the Bounty 2 to approach the USS Enterprise-B, since a Klingon ship that deep in Federation territory would likely disrupt the tenuous peace of the recently signed Khitomer Accords. (Star Trek novel: Engines of Destiny)
After Starfleet refused to participate in the invasion of the Cardassian Union in 2372 and the Federation Council condemned it, Chancellor Gowron withdrew the Empire from the Accords. (DS9 episode: "The Way of the Warrior")
Among the agreements of the Accords was a provision stating that diplomatic pouches were not subject to searches by security or military personnel; Ambassador Worf utilized this privilege to carry weaponry and classified Starfleet Intelligence equipment into the Klingon Great Hall. 
Following the formation of the Typhon Pact, the Federation and Klingon Empire invited the Imperial Romulan State, Cardassian Union, Ferengi Alliance and Talarian Republic to join in an expansion of the Accords to establish a strong counter-alliance to the Pact. Empress Donatra of the Imperial Romulan State and Ferengi Grand Nagus Rom immediately accepted the invitation. (ST novel: A Singular Destiny)
In 2399, after two decades of off-and-on war the Klingons and Orions launched a full-scale invasion of the Gorn Hegemony, claiming that the Gorn government and high command were infested with Undine, and requested the Federation join the war under the Accords. As in 2372, with no evidence supporting the Klingons' claims the Federation Council voted instead to condemn the invasion, and the Klingons withdrew from the treaty. Without the Accord restraining them, in 2404 Chancellor J'mpok invoked ancient, long-ceded territorial claims to the Hromi Cluster, demanding that all Federation citizens leave the region within three months, but Federation President Aennik Okeg threw the ultimatum in his face in 2405. J'mpok promptly ordered an invasion to forcibly eject the Federation, beginning the Federation-Klingon War of 2405-2410. (STO website: The Path to 2409)
The Federation and Empire agreed to a ceasefire in 2410 and resumed their alliance, with the Romulan Republic joining them in the Alpha Quadrant Alliance. (STO - "Solanae Dyson Sphere" mission: "Surface Tension"; STO video game: Delta Rising)
- Article I: Both Parties obligate themselves to desist from any act of violence, any aggressive action, and any attack on the each other, either individually or jointly with other powers.
- Article II: The Governments of the two Parties shall institute full diplomatic relations with each other. A parcel of land shall be delivered on each of the worlds, which will serve as center for government for each Party so that the other Party may establish an Embassy.
- Article III: Should one of the Parties become the object of belligerent action by a third power, the other Party shall in no manner lend its support to this third power, and will lend whatever aid and assistance to the other party it deems appropriate by the rules of its internal government.
- Article IV: Both Parties agree to provide humanitarian aid to each other.
- Article V: Both Parties agree that any former grievances they had with the other are now forgotten. If any individual under the rule of one Party commits an act of revenge or retribution on the other Party, that individual will be extradited to stand trial under the laws of the aggrieved Party.
- Article VI: Both Parties agree to the specifics of the following sections delineating conflict resolution, territorial definitions, trade laws, and all other provisions in this document. (ST reference: Federation: The First 150 Years)