The Treaty allowed unrestricted passage for all Klingon starships in Federation space, and vice versa. Under normal circumstances, such vessels could not be boarded or searched without cause. The Treaty, however, did possess a clause allowing health and safety inspections of vessels to verify that they were free of hazards which could affect the well-being of any persons on board.
The crew of the USS Enterprise-D conducted a health and safety inspection under the treaty in 2370 of a Klingon Toron-class shuttle operated by Koral. The use of the inspection clause was simply a ruse to gain access to the vessel to look for a portion of a missing Vulcan artifact, the Stone of Gol. The search did not turn up the artifact, as it was on Koral's person at the time. (TNG: "Gambit, Part II")