The police in Lucknow cracked down protesters using tear-gas and batons after vehicles parked outside a police-post were set on fire and stones thrown during a demonstration in the Uttar-Pradesh capital against the Citizenship(Amendment) Act. State-police chief OP Singh told news-agency PTI that cops had to fire tear-gas shells to control the situation in Madeyganj-area. About 20-people have been taken into custody, he added.