The First Assembly was a government that existed within the Tholian Assembly.
According to the Laws of the First Assembly, the Tholian race were prevented from colonization of the Shedai Sector. This long standing law prevented the species from mounting an adequate protection of that region of space in latter centuries.
By the 23rd century, Radkene objected to the law as he believed that the Klingon Empire did not exist when the First Assembly had ratified it as canon. Thus, the law spoke about the galaxy that was whilst he believed they should have ruled that currently existed. (VAN novel: Harbinger (novel))