While Transport Workers Union Local 234, the largest SEPTA union of around 5,000 employees who operatee most buses, subways and trolleys, has not yet gone on strike since their contract expired Sunday night, the potential strike is looming as negotiations continue. The union has been prepared to strike for a month. 

If a strike does occur, buses, subways (including the Market-Frankford line), trolleys and the Norristown high-speed line will not be operating, affecting hundreds of thousands of passengers. The Regional Rail, University City LUCY loop and CCT shuttles will continue to run. 

On Sunday, TWU Local 234 posted on their website after an unsuccessful day of negotiations, "SEPTA has replaced the question of if we strike with the question of when we strike."

The last SEPTA workers' strike in 2009 lasted for more than a week, affecting hundreds of thousands of riders.