The ULFA (I) has been collecting funds from tea gardens in Tinsukia district over the past few days.
The outfit has been serving extortion notes to several tea garden owners of the district.
Sources said some such tea garden owners have made complaints before the police, but many others have not divulged the matter due to their personal security.
Police sources said that the ULFA (I) rebels on November 23 sent extortion note to the manager of Cham Dang tea estate belonging to William Son Magor in the district demanding Rs one crore.
The outfit also served extortion note to the manager of Kanoh Pathar tea estate demanding Rs 40 lakh from the management of the tea garden.