Passport needed when Peninsular Malaysia's people go to Sarawak

Under a special arrangement agreed during the formation of Malaysia, the East Malaysia states of Sabah and Sarawak can retain their respective immigration control systems. As a result, a passport is required when traveling from Peninsular Malaysia to East Malaysia, as well as the mutual travel between the two states. Malaysian citizens from Peninsular Malaysia were required to present a Malaysian passport when travelling to East Malaysia from Peninsular Malaysia.

      

This agreement actually is for protecting people from Sabah and Sarawak.