Pro-government organisations and the leftist Workers' Party were arranging protests in 31 cities across the country, with the main one expected in the capital Brasilia.
Lula, who founded the Workers' Party and remains a heavyweight figure on the left, called for supporters to take to the streets on his Facebook page.
Similar rallies supporting Rousseff against impeachment proceedings in Congress saw some 270,000 people turn out on March 19, according to police estimates.
Rousseff is scrambling to rebuild support in Congress after her coalition's main partner, the centrist PMDB, voted Tuesday to quit.
Rousseff yesterday described the impeachment proceedings -- based on allegations that she illegally boosted government spending during her 2014 reelection -- as baseless and a "coup" attempt.
Although Lula is highly popular on the left, he has become a hate figure for the opposition and faces charges linked to a massive corruption probe at state oil company Petrobras.
