Rousseff's appointment of her embattled mentor as her chief of staff has triggered outrage among opponents, who filed some 50 court cases challenging the nomination over allegations that Lula was seeking ministerial immunity to avoid arrest in an explosive corruption scandal.

A Rio de Janeiro federal court ruling blocking him from taking up his new post was overturned on appeal, meaning he can join the government.

But dozens of similar challenges are pending, and the Supreme Court has yet to rule on the government's request to definitively settle the matter.

With Rousseff fighting a newly relaunched impeachment bid and financial markets apparently betting her government will collapse, the leftist leader's supporters began taking to the streets for demonstrations aimed at showing their strength.