A case has been registered against Karnataka Tourism, Ecology and Environment Minister Anand Singh for allegedly threatening a family, whose members later attempted to set themselves on fire, over a land dispute, police said on Wednesday. The FIR has been registered against the minister and three others following a complaint lodged by D Polappa, under the Prevention of Atrocities Against SC-ST Act, and sections 504 and 506 of the IPC, they said.