Claiming this in a statement, the CPI(M) also demanded an enquiry into the allegation by the Election Commission.
The Left party, which has put up Khemraj Chetry in the Tezpur seat, said even Congress has a history of taking help from banned militant group for an election.
"The Manisena Commission has stated that Congress had a secret understanding with DHD(Jewel) for the Dima Hasao election in 2007, although the ruling party did not get any benefit," CPI(M) Assam unit Secretary Uddhab Barman alleged.
"To have a free and fair election in the state, I request the Election Commission to enquiry the matter and take necessary steps," Barman said in the statement.