The strike also stopped the production of at least 70 per cent of the oil and gas from the more than 20 offshore rigs and onshore wells in the northeastern state of Rio Grande do Norte, Dantas said.
Union officials say 165 employees have been killed in the last seven years in accidents.
Petrobras' net income rose 58 per cent to 33.9bn reals ($14.2bn) last year amid an output increase of 4.3 per cent as global oil prices soared to more than $147 a barrel in July before falling to $54 on Monday.
Al Jazeera's Lucia Newman said the firm's ambitious plans for expansion were being hit by the global economic downturn just as workers were demanding a bigger share of profits.
The firm is third largest oil producer in the Americas and one of the 20 largest in the world.