Brazilian police detained six people as part of an investigation into suspected bribery at a unit of state oil company Petroleo Brasileiro.
Police carried out eight search warrants related to the scheme. Prosecutors say illegal payments were made by a contractor to a manager of Transpetro, a subsidiary of Petrobras, as the company is commonly known.
Transpetro did not immediately respond to a request for comment.
Prosecutors say the payments to the unnamed manager, which totalled 7m reais (€1.8m), occurred between 2009 and 2014. According to investigators, part of those bribes were then passed to Brazil's leftist Workers' Party.
The investigation unveiled on Tuesday follows revelations of a separate alleged scheme involving Transpetro and the Brazilian Democracy Movement Party (PMDB) of President Michel Temer.
In September, a Brazilian prosecutor charged six current and former PMDB senators of unduly receiving 864m reais in bribes, generating losses of 5.5 billion reais at Petrobras and 113m reais at the Transpetro subsidiary.
As part of the most recent investigation, police said the arrests are taking place in the states of Sao Paulo, Santa Catarina, Sergipe, and Bahia.
