Rashtriya Janata Dal (RJD) chief Lalu Prasad Yadav on Saturday urged Janata Dal (United) (JD(U)) co- founder and leader Sharad Yadav to take part in the fight against the Bharatiya Janata Party (BJP) and chief minister Nitish Kumar, who, he said, joined with "communal and fascist forces and betrayed the people's mandate."