Article 7 Chicago Convention

Cabotage

Each contracting State shall have the right to refuse permission to the aircraft of other contracting States to take on in its territory passengers, mail and cargo carried for remuneration or hire and destined for another point within its territory. Each contracting State undertakes not to enter into any arrangements which specifically grant any such privilege on an exclusive basis to any other
State or an airline of any other State, and not to obtain any such exclusive privilege from any other State.

See also: Article 6 Chicago Convention