Five houses belonging to Congress lawmakers were on Monday burned down by an angry mob in Manipur's Churchandpur district over the Inner Line Permit issue, officials said.The residence of Health and Family Welfare Minister Phungzathang Tonsing was among those torched.The mob also set afire the vehicle of Churachandpur Deputy Commissioner Lunminthang Haokip, and prevented fire engines from dousing the flames, even as police were forced to resort to a baton charge.However, none of the lawmakers were at their residences. They were all in state capital Imphal attending the special legislative assembly session.Officials said the mob was comprised of members of tribal students organisations protesting against the Manipur government's adoption of three landmark bills -- Protection of Manipur Peoples Bill 2015, Manipur Land Revenue and Land Reforms (seventh amendment) Bill 2015, and Manipur Shops and Establishment (second amendment) Bill 2015.The three bills were unanimously passed in the assembly after the ruling Congress signed an agreement with the Joint Committee on Inner Line Permit System (JCILPS) on August 25 to enact three laws to protect the interest of the indigenous people.However, tribal civil society groups opposed the introduction of the bills, saying they overlapped with some points in the Manipur Hill People Administration Regulation Act, 1947, meant to safeguard the interest of tribesmen in the hill areas of Manipur.