A builders' union is understood to be considering taking strike action over the working conditions on construction sites for World Cup stadia in Brazil.
Several construction workers have now died at venues connected with Brazil 2014 as the nation rushes to complete its venues on schedule.
Two were killed in an accident last month when a crane fell and destroyed parts of Sao Paulo's Arena Corinthians, where the tournament's opening game is due to take place on June 12.
Hours later, another worker died of a heart attack at a nearby site, with his family claiming that he had been overworked.
The body of 49-year-old Jose Antonio da Silva Nascimento was discovered at a new building that will host meetings during the World Cup.
His death may not be connected with the working conditions, but sister-in-law Priscila Soares told O Globo that he was under pressure and working a seven-day week because construction was behind schedule.