Negotiators for Philadelphia's transit system and the union representing 5,700 of its workers have been meeting to try to reach agreement on a new contract before a midnight Monday deadline.
SEPTA is the nation's sixth largest transit system. Officials say a strike by city bus, trolley and subway workers could begin Tuesday if no agreement is reached.
The agency 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.