A subway strike in São Paulo, Brazil, could hamper the commute for thousands of soccer fans traveling to and from the World Cup next week, and FIFA won't say what it plans to do about it.

São Paulo subway workers announced late Wednesday night they would strike indefinitely starting the next day. The strike was already causing headaches for the city of 20 million by Thursday.

A FIFA spokesman declined to discuss the strike when contacted by BuzzFeed, only saying that the body was "very optimistic and we think it's going to be a great World Cup."

"We can't speculate about the strike situation," the spokesman, who only gave his first name, told BuzzFeed. "Second, it's up to the local transport authorities to make the necessary arrangements for transport in the city."

"We can't comment on this because it's something that's being dealt with by São Paulo," the spokesman added.

The spokesman then asked BuzzFeed to only quote from a press release from FIFA. The release ran with the headline: "Nearly three million tickets for Brazil 2014 sold to date." The press release does not mention the strike.

The World Cup's opening match is scheduled to be played in São Paulo's Corinthians Arena on June 12 and the subway is the main mode of transportation serving the stadium. The São Paulo subway serves 4.5 million people daily — a number due to rise for the month of the World Cup.

Reports say commuters broke down barriers at the Corinthians Arena subway stop while 135 miles of bumper-to-bumper traffic built up around the city Thursday.

The striking subway workers reportedly want a salary increase of at least 10%. The union president said they already rejected an offer for an 8.7% increase.