Maria Figaro, spokeswoman for the subway workers union said the lines were being operated by management personnel and newly hired trainees.
''The strike will most likely continue until our demands are met,'' Figaro said.
She said the union reduced its initial demand, from a 16 to 12.2 percent wage hike, but the company insists it can only afford an 8.7 percent raise.
The subway strike in Sao Paulo illustrates the potential for disruptions during the World Cup, which opens here on Thursday. The more than 3.5 million people who use the city's public transit systems on weekdays faced chaos as subway lines operated in recent days with limited service.
The strike worries authorities because most soccer fans heading to the Itaquerao stadium for the opening match will need to use the subway.
Cup organisers have fretted for that a resurgence of mass anti-government protests could mar soccer's premier event, with all the world watching. But in recent weeks, strikes by public transport workers, police, teachers and others in several Cup host cities has proved more disruptive than anti-government demonstrations.
Unions across Brazil have used the World Cup as leverage to get concessions from authorities and so far, it's often worked. Federal police officers and garbage collectors in Rio de Janeiro were able to win better wages recently.
Unions argue that high inflation is eating away at workers' purchasing power. The government's statistics agency said Friday that the benchmark consumer price index rose 6.37 percent in the 12 months through May.
Other cities have also seen union action. Last Thursday, striking teachers in Rio de Janeiro blocked main roads during the evening rush hour, snarling traffic in that city.
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 Fortaleza, also a World Cup host city, brought widespread looting during two days.
A 48-hour strike by Sao Paulo and Rio de Janeiro bus drivers last month left hundreds of thousands of people unable to get to and from work, while civil police in 14 states went on a 24-hour work stoppage demanding higher wages. The police strike affected at least six cities hosting World Cup games: Rio de Janeiro, Sao Paulo, Salvador, Manaus, Recife and Belo Horizonte.
Federal police agents, who oversee immigration at international airports, and state police officers responsible for keeping order on the streets have said they may strike during the World Cup despite a Supreme Court injunction ordering them not to halt work during the tournament.
The strikes have overshadowed earlier worries about protests fed by anger over the billions spent to host the World Cup while Brazil's schools, health system and public transit have widespread problems.
Huge protests last year took over streets in dozens of cities during the Confederations Cup, international soccer's warm-up tournament for the World Cup. On just one night, a million people were out in the streets across Brazil to join in demonstrations.
The almost daily protests being held now in the lead up to the main tournament are far smaller than those a year ago.