Members of the SMART Local 1594 spent the day voting on the issue. The union is made up of hundreds of bus, trolley and train operators who work at 69th Street Terminal in Upper Darby.
Union leaders say workers are not walking off the job, as negotiations continue.
Their contract expired Nov. 19.
This comes as another union, Transport Workers Union Local 234, is set to resume contract talks on Monday. They, too have threatened to strike. The union represents about 5,000 workers, including operators of Philadelphia's buses, subways, and trolleys.
The two unions were in a similar spot around this time last year, but were able to reach a deal with SEPTA. The one-year agreement included a 5% wage increase and safety improvements, such as bulletproof enclosures for drivers.
A strike would not impact Regional Rail riders, who have already been dealing with more than six weeks of delays and cancellations due to federally mandated emergency inspections.
To learn more about any possible impacts if a strike does happen, click here.