The Workers Party has distanced itself from the senator since his arrest. An internal investigation will decide whether Mr Amaral should be expelled.
The senator had been secretly recorded apparently discussing plans to help a detained official flee the country in return for not implicating Mr Amaral in the scandal.
The official, Nestor Cervero, was accused of masterminding the corruption scheme. He signed a plea bargain agreement with prosecutors.
`No solidarity`
At the time of Mr Amaral`s arrest, the president of the Workers Party, Rui Falcao, published a statement saying he was "perplexed by the facts" that led to the arrest.
"None of the acts attributed to the senator is connected to his activities for the party. "For that reason, the Workers Party does not feel obliged to lend him any solidarity," added Mr Falcao.
Other influential members of Brazil`s Workers Party, including the former President Luiz Inacio Lula da Silva, have openly criticised the senator.
One of Brazil`s richest men, banker Andre Esteves, was also arrested on 26 November as part of the same operation. Federal police said he was also involved in the plot to help Mr Cervero flee to Spain.
Mr Esteves is Brazil`s 13th richest man, worth an estimated $2.5bn (£1.7bn), while Mr Amaral is the first sitting legislator to be detained in the scandal.
Both men deny the charges. President Dilma Rousseff has not been implicated in the scandal, but the allegations against senior members of the Workers Party have led to a sharp drop in her popularity since she was re-elected last year.
On Wednesday, the speaker of the lower house of Congress opened impeachment proceedings against President Dilma Rousseff.
The process is based on allegations Ms Rousseff broke the law in managing last year`s budget.
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