(Adds details of case, comment from union)
SAO PAULO, April 17 (Reuters) - A Brazilian court has ordered state-controlled oil company Petróleo Brasileiro SA to suspend the sale of its stake in an exploratory block to Norway's Statoil ASA after a union argued there should have been an open bidding process.
Petrobras, as the company is known, said in a securities filing on Monday that the deal for its stake in the BM-S-8 region known as the Carcara field was approved by regulators.
Half of the $2.5 billion in proceeds were due when the deal closed in November, and the company said it had used those funds to repay debts. Petrobras said it would take legal measures to defend its interests.
The sale of the 66 percent stake in the offshore prospect was the first major pre-salt asset sold as part of a divestment plan that now aims to raise $21 billion in two years for Petrobras to pay down its debts.
The National Federation of Oil Workers said it had filed the lawsuit because Petrobras, as a state-controlled enterprise, is required to hold an open bid for any asset sale.
A Statoil representative said the Norwegian firm would not comment on the matter because it had not received an official notice of the decision. (Reporting by Marta Nogueira and Tatiana Bautzer; Writing by Brad Haynes; Editing by Cynthia Osterman and Lisa Shumaker)