Negotiators for the Philadelphia transit system and a union representing 5,700 workers have been meeting to try to reach agreement on a new contract before a midnight Monday deadline.
The Philadelphia system is the nation's sixth largest. Officials say a strike by city bus, trolley and subway workers could begin Tuesday if no agreement is reached.
The Southeastern Pennsylvania Transportation Authority has urged riders to come up with alternative plans should a strike occur. A strike would affect bus, trolley and subway lines but not regional rail lines and service outside the city.
More than 60,000 public, private and charter school students use the transit system.
Union officials have cited pension and health care but also some non-economic issues.
A 2009 strike by SEPTA workers lasted six days.