Work permit in Nepal for Indian citizens

Are Indian citizens required to obtain work permit in Nepal? Are they exempt based on Indo Nepal Treaty of 1950?

A large number of Indian workers are working in informal sectors and as laborers in the industries or retails businesses without obtaining work permits and some argue that Indian nationals are not required to obtain work permits as their migration to and employment in Nepal are regulated by the Indo-Nepal Peace and Friendship Treaty 1950. How do we interpret provision of the treaty and what is the practice?