The militants first exploded a powerful grenade and opened fire at the workers at Thingen area yesterday before escaping to nearby jungles.
Personnel of India Reserve Battalion, who were guarding the area, returned the fire and the exchange of fire lasted for over an hour, the police said.
No monetary demand had been made by the militants from the construction company and the motive behind the attack was not known, the police said.
In another incident, there was a heavy exchange of fire between two factions of Kuki militants at Phaiton area in Tamenglong district during which a militant was injured last evening, the police said.