Sao Paulo's metro workers are striking for a fifth day, which could potentially cause chaos for the World Cup's opening game in three days.
Another vote on the strike is expected at 3pm following a rally held by workers.
"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," the union said in a note on Sunday.
The opening game of a World Cup is generally reserved for a smaller number of fans, sponsors, hospitality representatives and commercial VIP's - meaning Fifa will be keen that the crisis is solved urgently.
More top news
Tony Blair has said Leave campaigners are focusing on immigration "because they've lost comprehensively the debate on the economy".
NBA player Bryce Dejean-Jones has been shot dead after breaking into an apartment he believed to be his girlfriend's, according to police.
Nineteen people have been rescued from the English Channel after the inflatable boat they were in started taking on water.