The share offering of the 2.3 percent stake owned by Caixa in Petrobras, as the oil company is known, depends on the publication of a new presidential decree authorizing the sale, the sources said, asking not to be named as the plans had not been made public.
President Jair Bolsonaro has already signed a first decree authorizing Caixa to sell its Petrobras stake, but the decree had technical mistakes and needed to be republished, they said.
Once the new decree is signed, Caixa will hire investment banks to help manage the secondary share offering.
Press representatives at Caixa Federal declined to comment.
Caixa plans to use the proceeds to pay off roughly 40 billion reais in convertible bonds sold to the Brazilian government between 2007 and 2013.
Petrobras common shares were up 1.15 percent at 30.86 reais on Tuesday in Sao Paulo trading, and has accumulated a 36 percent gain over the last 12 months.
The sale of the Petrobras stake will be the second divestiture led by Caixa since Chief Executive Pedro Guimaraes took the helm at the state bank last month, after the sale of a 2.4 billion reais stake in reinsurer IRB Brasil Resseguros SA. The IRB share offering will be priced later on Tuesday.
The IRB shares are owned by a government fund responsible for financing education and managed by Caixa.
Caixa owns 3.2 percent of Petrobras common stock directly and 1 percent of non-voting capital.
Both transactions will be led by Caixa's recently created investment banking unit, with around 30 bankers recruited internally.
Guimarães has said he intends to list at least four Caixa units: asset management, credit cards, lottery and insurance.
Guimaraes recently appointed new senior management officials at Caixa. Andre Laloni, former head of UBS AG in Brazil and the Southern Cone, is the new chief financial officer, while former Banco Santander Brasil SA executive, Luciane Ribeiro, will lead Caixa's asset management unit.
(Reporting by Tatiana Bautzer and Carolina Mandl; Editing by Bernadette Baum)
By Tatiana Bautzer and Carolina Mandl