Roads leading to Sonko's home in Dakar were closed off by barricades and police in anti-riot gear Friday, and supporters who tried to get near the building were firmly told to turn back, AFP reporters saw.
Sonko had called for demonstrations on Friday to protest at a decision to bar a list of candidates for Senegal's legislative elections on July 31 -- a move that also bans him and other opposition figures from contesting the ballot.
Sonko and his allies have vowed to push ahead with the protest on Friday, despite a ban on the rally announced by the prefect on the grounds of public order.
"The demonstration is on, it will definitely take place," Ousseynou Ly, spokesman for Sonko's PASTEF party, told AFP.
Some figures have appealed for dialogue, recalling the violence that erupted in March last year, claiming around a dozen lives, after Sonko was accused of sexual assault.
The candidates' list, put forward by an opposition coalition called Yewwi Askan Wi, was scratched on the orders of the interior ministry on technical grounds.
The country's highest court, the Constitutional Council confirmed the ministry's decision.
Sonko says the bar is the result of political interference, a charge rejected by the government.
The legislature has 165 seats. Of these, 53 are chosen on the basis of national lists and 97 on the basis of a majority vote among the country's departments, while 15 are chosen by the Senegalese diaspora.
The ban on Yewwi Askan Wi's list applies specifically to first-choice candidates for seats contested by national lists. The coalition can still compete using alternate candidates.
Two other prominent opponents of President Macky Sall -- former Dakar mayor Khalifa Sall, who is not related to the head of state, and former minister Karim Wade, the son of an ex-president -- have seen their political careers truncated by legal cases.
Senegal has a long reputation as a beacon of stability in West Africa, where political turbulence is common.