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Another vote on the strike was scheduled for Monday at 1pm (local time), after a rally in downtown Sao Paulo in which they will be joined by homeless' workers and other social movements.
"The (metro workers') union sent an official request to President Dilma Rousseff asking her to help the category reopen talks with the (Sao Paulo) state government," which controls the subway system, the union said in a note on Sunday.
A court on Sunday set a 500,000 reais penalty ($223,000) for each day they stay off work from Monday. It also declared the strike illegal, paving the way for state-owned Companhia do Metropolitano de Sao Paulo to lay off striking workers.
Metro workers' demand a 12 percent pay rise, but Metro has offered 8.7 percent.
With major subway lines closed since Thursday, commuting in Brazil's largest city has been chaotic.
The strike snagged several FIFA officials in over two hours of traffic as they arrived for a conference ahead of the World Cup last week, which kicks off with a Brazil v Croatia match in Sao Paulo on Thursday.
On Friday, police used tear gas to break up a demonstration blocking access to one metro station.
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 from homeless groups and striking workers using the backdrop of the World Cup to press their causes.