The group of armed Maoists attacked the camp office of GSR construction company last night. The labourers resting at the camp were also beaten up, Superintendent of Police Kailly Dhuran said.
Later, they torched four machines including one mixer before leaving the place.
They also distributed leaflets claiming non-payment of levy as the reason behind the attack, police said.
Police have cordoned off the entire area and a search has been launched for the ultras.