The Sao Paulo metro is the main transport link to the economic capital's host stadium, and the indefinite strike could pose a massive logistical headache for organizers -- as well as the 4.5 million passengers who use it daily.
Frustrated commuters broke entrance grilles at the station that serves the stadium, Corinthians Arena, forcing system operators CPTM to take emergency measures to open it.
With more people using their cars, bumper-to-bumper traffic stretched for up to 209 kilometers, the worst congestion so far this year and the third worst ever recorded in the sprawling mega-city of 20 million people. The strike affected three of the city's five subway lines, a system employee told AFP.
The unrest ballooned into nationwide demonstrations against the more than USD 11 billion being spent on the World Cup.
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A million protesters turned out last June during the Confederations Cup, a World Cup dress rehearsal.
The protests turned violent at times, overshadowing the tournament and raising fears of a repeat this year.
The movement has since lost momentum, but today's transportation chaos risks rekindling anger with one week to go to the opening ceremony and match.
Workers went on strike at midnight after negotiations on a salary increase fell through. They rejected an offer of 8.7 per cent, insisting on at least 10 per cent, said the president of their union, Altino Melo dos Prazeres.
"If there's money for the Itaquerao (the nickname for Corinthians Arena) and the World Cup, how is it they don't have any money for public transportation?" Prazeres was quoted as saying by newspaper O Estado de Sao Paulo.