An interstellar agreement that outlawed subspace weapons because of their unpredictable effects, which the Son'a violate when they attack the Enterprise-E in Star Trek: Insurrection.
The Second Khitomer Accords are a treaty among the major powers that followed the original Khitomer Accords between the Federation and the Klingon Empire. Among their terms is a ban on subspace weapons, which can tear lasting rifts in space.
The treaty is named in Star Trek: Insurrection. As the Enterprise-E, commanded by Riker, races out of the Briar Patch to tell the Federation Council about the plot against the Ba'ku, two Son'a ships attack it with an isolytic burst. The officers on the bridge recognise the weapon at once as one banned by the accords.
The tear begins to chase the ship's warp core. Riker has the core ejected and detonated to seal it, and then turns on the Son'a using the gas of the Briar Patch itself. The attack shows how little the Son'a care for the law.