At least Three Union Members Were Injured In The Sao Paulo Clash, 

Brazilian police used tear gas, rubber bullets and stun grenades to disperse striking workers inside a subway station on Friday, adding to fears that labor unrest could disrupt the World Cup that opens here in six days.

At least three union members were injured in the Sao Paulo clash, said Paulo Iannone, a union spokesman.

Operators of the subway and overland trains were in the second day of a strike for higher wages, with no indication that it would end soon. Late Friday, officials and the union representing workers said they had not reached an agreement to end the strike and it would continue into Saturday.

That's worrying for authorities because most soccer fans heading to Thursday's opening Cup match in Sao Paulo will need to use the subway.

Cup organizers have fretted for a year that a resurgence of mass anti-government protests could mar soccer's premiere event, with all the world watching.

But in recent weeks, a series of strikes by public transport workers, police, teachers and others in several Cup host cities has proved more disruptive than demonstrations.

If such strikes continue, "there will be chaos during the World Cup," said Carla Dieguez, a sociologist at Sao Paulo University's School of Sociology and Politics.

"What we don't know is how long the (subway) strike will last and if workers in others cities where games will be held will also go on strike," she said.

Unions across Brazil are using the leverage of the World Cup in an effort to get concessions from authorities, as has happened before other big sporting events. Ahead of South Africa's World Cup in 2010, bus drivers went on strike.

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.