So far, it's often worked, as in the case of federal police officers and garbage collectors in Rio de Janeiro who have won better wages recently.
Unions argue that high inflation is eating away at workers' purchasing power. On Friday, the government statistics agency said the benchmark consumer price index rose 6.37 percent in the 12 months through May.
Justice Minister Jose Eduardo Cardozo made an appeal to national pride to get strikers to return to work in time for the Cup.
"We want to feel proud of our country," Cardozo said. "On and off the pitch we must show what we are capable of."
Unions in Brazil are strong and often strike to demand higher wages and better working conditions.
Brazil's former President Luiz Inacio Lula da Silva got his start as a fiery steel workers union leader who led massive strikes that weakened Brazil's military dictatorship. Silva went on to start the ruling Workers Party, which has strong ties to unions, though they've often been strained since the party took the presidency in 2003.
It's not just Sao Paulo that's seeing union action.
Striking teachers in Rio de Janeiro blocked main roads during Thursday's evening rush hour, snarling traffic.
A two-day walkout in April by state police officers in the northeastern World Cup host city of Salvador led to a spike in homicides and robberies. One week earlier a police strike in the city of Fortaleza, also a World Cup host, brought widespread looting during two days.
