The three districts are Cachar, Hailakandi and Karimganj.
"On the occasion of the celebration of Namami Barak, the Government of Assam has declared a public holiday on November 20, 2017 within the jurisdiction of three districts of Barak valley," an official release said.
It also said that all offices under Government of Assam, revenue and magisterial courts and educational institutions in the three districts will remain closed.
Assam Chief Minister Sarbananda Sonowal yesterday inaugurated 'Namami Barak' festival at Silchar.