Last-ditch negotiations are scheduled Friday to try to avert a walkout that could halt commuter trains serving the Philadelphia area this weekend.
Federal mediators have asked the Southeastern Pennsylvania Transportation Authority to meet with the two unions representing about 400 engineers and electricians.
Stephen Bruno, vice president of the Brotherhood of Locomotive Engineers and Trainmen, said workers will strike at 12:01 a.m. Saturday if no deal is reached. He says "a chasm" separates the parties.
Thirteen regional rail lines serve about 126,000 passengers each weekday in the Philadelphia suburbs of Pennsylvania, New Jersey and Delaware.
Buses, trolleys and subways into Philadelphia would still operate in the event of a walkout.
If a walkout occurs, riders will be directed to the nearest non-commuter rail transit hub, SEPTA spokeswoman Jerri Williams said.
A spokesman for the International Brotherhood of Electrical Workers did not return a call for comment Thursday.
The engineers have been working without an agreement since 2010, while the electricians' contract expired in 2009. Their negotiations with SEPTA have been supervised by federal mediators for the past four years.
The conflict came to a head this week after SEPTA announced it would impose a deal beginning Sunday. Terms include raising electrical workers' pay immediately by an average of about $3 per hour; the top wage rate for locomotive engineers would rise by $2.64 per hour.
"The contract that we've given them is fair and fiscally responsible," Williams said.
The agency said the raises are in line with those received by other unionized SEPTA employees, but Bruno disagreed. He said SEPTA offered the engineers raises of 11.5 percent over five years, but workers are seeking at least 3 percent more.
"There haven't been any consequences for SEPTA's intransigence," Bruno said. "We don't think they've been forthcoming with their best offer."
One wild card is a provision allowing the governor of an affected state to request a Presidential Emergency Board to intervene in the bargaining. That could prevent a strike for up to 240 days.
Spokesmen for Pennsylvania Gov. Tom Corbett, New Jersey Gov. Chris Christie and Delaware Gov. Jack Markell did not return requests for comment on Thursday.
Amina Thompson-Wright, 35, of Philadelphia, takes a regional rail to her city job as a child-abuse investigator. Her husband takes their one vehicle to work.
"It would definitely put me in a bind to look for other forms of transportation," said Thompson-Wright, who would try to carpool with co-workers.
The last regional rail strike, in 1983, lasted for more than three months.