"The people have to mobilise to support Ousmane Sonko in this fight," Khalifa Sall, one of the coalition chiefs, told a press conference a day after Sonko was handed a six-month suspended term that could jeopardise his bid for the 2024 elections.
Sall joined other heads of the Yewwi Askan Wi alliance in urging followers to turn out in force for an already-scheduled rally due this Friday, and for another protest a week later, on May 19.
Senegal is traditionally a beacon of stability in troubled West Africa, but in recent years has been buffeted by turbulence that has at times turned deadly.
But his candidacy has been clouded by Monday's conviction, which saw an appeal court increase a sentence of two months suspended, handed down in March, for defaming Tourism Minister Mame Mbaye Niangtou.
The court also ordered Sonko to pay 200 million CFA francs (around $330,000) in damages to Niang.
Sonko is also facing trial later this month for alleged rape and death threats over a complaint filed by an employee at a beauty salon where he went for a massage.
He says he is the victim of a government plot to scupper his candidacy.
In 2021, the rape charge against him helped trigger riots that left at least 12 people dead.
Political tensions have also been stoked by Sall's refusal to rule out running for a third term as president, a move his opponents say would be unconstitutional.