Mauro Cunha, who represents minority shareholders on the 10-member board, said he read news reports that former Banco do Brasil CEO Aldemir Bendine, a confidant of Brazilian President Dilma Rousseff, would take the helm of Petrobras before the board had even had a chance to vote on the appointment.

Seven members of the state-controlled oil company's board are appointed by the government while three are independent.

"We have seen today an episode of disrespect for the board of directors of Petrobras," Cunha said in a statement. "Once again the controlling shareholder (the government) has imposed its will over the interests of Petrobras, ignoring the appeals of long-term investors," he added.

Silvio Sinedino, who represents the company's unionized employees, said he voted against Bendine and five other senior appointments in protest over the political nature of the appointments and failure to fully consult the board and company workers.

He called on the company to set objective criteria for naming senior executives. He blamed a history of political interference in the selection of top-level Petrobras managers for the corruption scandal that has recently hobbled the company, cut it off from financial markets, forced it to halt dozens of projects and led to the layoff of thousands of workers.

Cunha, who has previously complained that non-government board members are not given enough time or material to make sound decisions on company policy, said he was reluctant to record his comments during the board meeting because he "ran the risk of suffering retaliation, as he has suffered in the past."

"As the securities filing announcement said, the decision was by a majority and not unanimous, from which you can conclude the position of this board member," he wrote.

(Reporting by Jeb Blount and Marta Nogueira; Editing by Christian Plumb)