Brazilian President Dilma Rousseff's approval rating plummeted to a new low after Sunday's massive demonstrations protesting against corruption and calling for her impeachment, a new poll published Wednesday said.

The survey by the Datafolha polling institute showed that the president's popularity dropped even among Brazil's poorest, where her support has been always been strong.

Sixty-two percent of respondents said Rousseff's government was "bad" or "terrible," compared with 44 percent a month ago. Thirteen percent of respondents rated her government as "great" or "good."

Datafolha interviewed 2,842 people March 16-17. The poll had a margin of error of 2 percentage points.

It was the worst popularity rating for a Brazilian president since 1992 when then-President Fernando Collor was impeached for corruption.

Sunday's protest marches in more than 150 cities were sparked by anger over a sprawling corruption case involving Petrobras, Brazil's state-owned oil company.

Federal prosecutors say they've uncovered Brazil's biggest graft case yet in a kickback scheme at Petrobras, with at least $800 million in bribes paid by construction and engineering firms to politically appointed former executives at the oil company, all in exchange for winning inflated contracts.

Investigators say some of the money was funneled back to the campaign coffers of the Workers' Party and its allies. Dozens of congressmen and some former executive branch officials, including two former chiefs of staff to Rousseff, are under investigation.

The president, who served as chairwoman of Petrobras' board during several years when the graft occurred, is not implicated.