SAO PAULO (AP) — Brazil's Supreme Court voted unanimously Thursday to allow corruption charges against a key congressional leader in a step that could weaken efforts to impeach President Dilma Rousseff.

All 10 justices at the session voted to proceed with charges against Eduardo Cunha, the head of the lower house of Congress who is accused of taking $5 million in bribes involving a contract by state oil company Petrobras. The 11th justice was out of the country.

Under Brazilian law, charges against federal congressmen and other top government officials can be filed and judged only by the Supreme Court. Thursday's decision marked the first time the Supreme Court has authorized charges in connection with the wide-ranging "Car Wash" investigation into corruption at Petrobras.

Cunha is one of the biggest names implicated in the scandal, which prosecutors allege involved billions of dollars in bribes. He is also a sworn enemy of Rousseff, having authorized the opening of impeachment proceedings against her late last year over allegations she violated fiscal responsibility laws.

Analysts said the Supreme Court's move could undermine the impeachment effort.

"This means that Dilma's accuser is no longer on the offensive but rather on the defensive," said Pedro Fassoni Arruda, a professor of political science at Sao Paulo's Pontifical Catholic University. "The government can use that as a trump card in the sense that they can say that the person who is accusing the president of having committed a crime probably committed a crime himself."

"This could change the balance of power between the government and the opposition, fortifying the government and weakening those who support Dilma's impeachment," he said.

Rousseff said Thursday that fighting corruption was among her government's top priorities.

"No government has cracked down as hard and efficiently against corruption as mine. And it will continue to be that way," Rousseff said at the swearing-in ceremony for Brazil's new justice minister, solicitor general and comptroller general.

Prosecutors allege Cunha accepted $5 million in bribes between 2006 and 2012 in connection with the construction of two Petrobras drilling ships. He is charged with corruption and money laundering.

Cunha has denied any wrongdoing. After the Supreme Court session began Wednesday, he told reporters: "Truth is on my side. I am innocent."

The Supreme Court has not yet weighed in on whether Cunha will be able to continue as head of the lower house and serve out the more than two years that remain of his term representing Rio de Janeiro state. Attorney General Rodrigo Janot has asked the justices to remove Cunha from office, but the court has not yet taken up the matter.

Thursday's decision was the second major blow for Cunha in two days. On Wednesday, the lower house's ethics committee approved an investigation into whether he should be stripped of his post for lying to a congressional hearing by denying he held bank accounts overseas. Swiss prosecutors later located accounts held by Cunha. The speaker had successfully blocked earlier attempts to open the probe.

Prosecutors in the Petrobras corruption case say more than $2 billion was paid in bribes by businessmen to obtain contracts with the oil giant. Investigators also have said that some of the money made its way to several political parties, including the governing Workers' Party.

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Associated Press writer Jenny Barchfield in Rio de Janeiro contributed to this report.