The strike is looking like a huge headache for the authorities because the subway is the main means of transporting thousands of fans to Thursday's opening game between Brazil and Croatia at the country's iconic Maracana stadium about 12 miles east of central Sao Paulo.
Riot police firing tear gas pushed about 100 striking workers out of the station as the strike threw Sao Paulo's congested traffic into chaos for a fifth day. Only about half of the city's subway stations were operating.
"This is the way they negotiate, with tear gas and repression," said Alexandre Roland, a union leader, after confronting riot police.
The striking workers marched towards the city centre, where they planned to join a wide-ranging rally by a range of activist groups, including homeless workers demanding low-cost housing and a group calling for free public transport.
Mr Roland said the strike would continue beyond the tournament's opening game unless the government met the workers' demands for a 12 per cent pay increase.
At the weekend a Sao Paulo labour court fined the union more than £100,000 for the first four days of the strike and said it would add £130,000 for each additional day the stoppage continued.
The government-controlled company that runs the subways is offering staff an 8 per cent pay increase and says it cannot go higher because fares to commuters have not been raised for two years.