Brazilian police fired tear gas at protesters during violent scenes in Sao Paulo less than a week before the city hosts the first match of the World Cup.
An indefinite strike by subway workers led to the closure of several stations on Friday and local television stations showed images of police beating the workers with batons, raising fears of unrest during the showpiece tournament.
Traffic delays as a result of the strike held up Brazil's team bus as they travelled to the stadium today for their friendly against Serbia.
Last summer during the Confederations Cup, more than a million Brazilians took to the streets to protest against the spiralling cost of staging the World Cup while demanding improved healthcare and education.
The nationwide demonstrations 12 months ago began in Sao Paulo over an increase in bus fares and Brazil is braced with the possibility of more anti-government protests, with organisers criticised over poor planning, late stadium delivery and infrastructure delays.
Brazil host Serbia on Friday before the country's biggest city hosts the first match of the World Cup, when Brazil take on Croatia on June 12.