A transit strike in Philadelphia has left hundreds of thousands of commuters stranded, threatening to paralyze the region for days — and the standoff between the union and the Southeastern Pennsylvania Transportation Authority could become an even bigger problem if it continues through Election Day.

When workers’ existing contract agreement with SEPTA expired at midnight following months of unsuccessful negotiations, leaders of TWU Local 234 called a strike. The union represents more than 4,700 SEPTA workers, including bus, train and trolley operators.

SEPTA buses, trolleys and subways provide about 900,000 rides a day.

“SEPTA negotiators stand ready and willing to continue bargaining,” SEPTA said in a statement Tuesday morning. “The Authority urges [union President Willie Brown] and TWU leadership to return to the bargaining table to negotiate an agreement that will end a severely disruptive work stoppage.”

SEPTA officials argued that the union is at fault for the breakdown in negotiations, saying that Brown “walked away from a contract offer that would have provided his members pay raises, enhanced pension benefits, maintained health care coverage levels and continued job security, while also remaining fair and affordable for the taxpayers and riders who fund SEPTA.”

Union leaders had warned the public in recent weeks about the potential of a strike if SEPTA officials did not address workers’ concerns about pensions and health care. In an update posted Saturday on the TWU Local 234 website, the union said that SEPTA negotiators “stormed out” of a meeting.

“Since negotiations broke down, the Union has been trying to get SEPTA back to the table to discuss economic issues, such as pension reform, health care and wage improvements,” the union wrote in that statement. “However, SEPTA is refusing to present a reasonable economic package. Instead, they are opposed to any and all improvements in our pension, while pushing a hard line on health care concessions.”

“As we’ve been saying,” the statement added, “it’s time to get ready to rumble. Our jobs and our livelihoods are on the line. Nothing is more important. We must have the will to fight.”

According to the Philadelphia Inquirer, the strike caused major paralysis during the Tuesday morning commute, with roads across the city backed up due to people choosing to use their cars to get to work.

If the strike continues through next week, it could have a significant impact on the election: Thousands of Philadelphia residents may have no means to reach their polling place.

And Pennsylvania is a battleground state in the presidential election, which could add to the urgency of finding a solution to the transit shutdown before next week.

SEPTA officials said in their statement Tuesday that if the strike looks as if it will continue through Nov. 8, the agency will pursue legal action to force the union to lift the strike for Election Day.

“If we foresee an agreement will not come to pass, SEPTA intends to seek to enjoin the strike for November 8th to ensure that the strike does not prevent any voters from getting to the polls and exercising their right to vote,” the agency said in its statement.