The 'Tau Ceti Accords were a set of peace agreements between Vulcan and Andoria signed sometime before 2151. Among other things, it prohibited Andorian presence on planet Coridan. The Andorian Imperial Guard, lead by Shran, violated these accords in 2151.
Notes
The Tau Ceti Accords may have been the peace treaty referred to in ENT:"Fallen Hero". In the episode, Velar negotated the first treaties with the Andorians in 2062.