Willie Brown, president of the Transport Workers Union Local 234, said the 4,700 workers voted overwhelmingly to allow him to call a strike if negotiations with the Southeastern Pennsylvania Transportation Authority fail. Talks are slated to resume Monday.
Brown said he hoped a walkout would not affect the series, but he said workers have been without a contract since March and have not had a raise since December.
"This is the last week we're going to work without a contract," Brown said, while vowing to "leave no stone unturned" to reach a deal.
SEPTA spokesman Richard Maloney said he hopes an accord can be reached quickly.
"We made a lot of progress last week, and there's no reason why in next couple of days this shouldn't be done," he said.
Maloney said the company would have a contingency plan but declined to discuss details.
"It's too early for that," he said. "Our main concern should be getting a contract negotiated and signed, and that's our total focus."
A strike by subway and trolley operators, bus drivers, and mechanics would affect the Broad Street subway line from the center of Philadelphia 4 miles south to the sports stadiums. Also affected would be the Market-Frankford line from the city's northeastern section to the western suburbs, as well as surface trolleys and buses throughout the city.
The third and fourth games of the World Series are scheduled for Saturday and Sunday in Philadelphia, and a fifth game, if necessary, would also be in the city Monday. In addition, the Philadelphia Eagles are scheduled to play the New York Giants on Sunday afternoon.
A seven-day walkout by the union idled buses, subways and trolleys in 2005. SEPTA's commuter rail service would not be halted since its workers are represented by a different union.