The 18 seats are part of 59 constituencies in which six Left parties will contest.
CPI will go to the people appealing for strengthening the third alternative force barring Congress and BJP, Mahanta told reporters here.
Alleging that Congress is corrupt and BJP is communal, the CPI leader claimed BJP with the help of capitalists will display money power in the next month's election.
Assam will go to the two-phase polls on April 4 and 11 for the 126 Assembly constituencies.