They have added the name 'Lula', after Luiz Inacio Lula da Silva was jailed last weekend.
The move, in tribute to the former president, was led by the head of the party, Gleisi Hoffman.
She will now be known as Gleisi Lula Hoffman in official Congress documents and on the electronic voting board.
The party's leader in the lower house, Paulo Pimenta, followed her example and is now called Paulo Lula Pimenta.
Party colleagues followed their lead in droves, but so did some legislators from right-wing parties.
They are adding Judge Sergio Moro - who convicted Lula - to their names.
The former president began a 12-year sentence for corruption on Saturday.
Lula says the charges against him were politically motivated.
BBC
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