Reports suggested around 300 people at the Ana Rosa subway station in downtown São Paulo clashed with officers wielding metal shields.
The protest was to support metro workers who are striking in support of an inflation-busting wage claim.
Subway workers went on strike in São Paulo for a fifth day yesterday even after a court ruled the stoppage illegal, spreading chaos across Brazil’s biggest city.
Further action may trigger more record traffic jams in the city of more than 20 million.
Striking staff burned rubbish bags in protest at the detention of several subway union leaders.
“The World Cup is not an excuse for us” to strike, Paulo Pasin, president of Fenametro, the country’s nationwide union of subway workers, claimed at Ana Rosa. “We want to reopen negotiations.”
The World Cup kicks off on Thursday as Brazil and Croatia meet at the Arena Corinthians stadium.
Geraldo Alckmin, governor of the state of São Paulo, warned of massive dismissals following the labour court ruling on Sunday that the strike is illegal.
Analysts say São Paulo is gradually becoming a battlefield for dissenting political views, hampering the city’s economy and creating a climate of unease ahead of the World Cup.
Frustration with broken promises and the ballooning cost of new World Cup stadiums contributed to widespread protests that drew over a million Brazilians into the streets during a warm-up tournament last year.
This year, the largest demonstrations so far have been by homeless groups and striking workers using the backdrop of the World Cup to press their causes.
Workers want a 12 per cent pay rise, with the state’s subway company offering 8.7 per cent.
With major subway lines closed since Thursday, commuting in Brazil’s largest city has been highly chaotic.
“This whole thing is making my life hell. Many times during the day I have to switch buses and vans. I have missed work – and I know am not the only one,” Djalma Melo, who works as an office assistant, said near Ana Rosa station.
Police patrols were parked outside several other subway stations in São Paulo’s west and south-east corners yesterday, however, no incidents were reported.