Brazil's top court has suspended Lower House Speaker Eduardo Cunha from his mandate, following a request by the country's attorney general, officials say.
He has been accused of trying to obstruct corruption investigations against him and intimidate congressmen.
Mr Cunha is an outspoken critic of President Dilma Rousseff and has led an impeachment drive against her.
In a BBC interview, Ms Rousseff has vowed to "keep fighting".
She is likely to be suspended from office for 180 days in a Senate vote next week.
Mr Cunha is formerly accused of bribery and money laundering as part of Operation Car Wash, or Lava Jato, which looks into a corruption scheme at the state-owned oil company, Petrobras.
He is accused of taking $5m (£3.2m) in bribes to secure contracts with the company. He denies the allegations.
Under Brazil's constitution, he was the third in line for the presidency.
Mr Cunha has not commented on his suspension.
He is a major figure in Vice-President Michel Temer's PMDB party.
If the Senate decides to open an impeachment trial against Ms Rousseff, Mr Temer will take over as interim president.
Ms Rousseff has accused Mr Temer and Mr Cunha of being the ringleaders of the "coup" attempt against her. She is accused of manipulating the federal budget, which she denies.
Waldir Maranhao, also under investigation by Operation Car Wash, is to become the next Speaker of the House.