Yes. As per the local taxi associations laws of Tawang, vehicles outside of Tawang are not permitted to visit Bum La Pass and the adjacent areas. So, you will have to hire a local taxi for that day.
We usually keep this as optional (and don�t include the cost of the additional taxi in our package) as some guests choose to skip the sightseeing of Bum La. So, we let the guests decide, after reaching Tawang, and if they choose to go for it then we help them in arranging a local taxi in Tawang.