Three other contracts for suburban bus drivers, mechanics, and clerical workers expire April 1 and April 7. The TWU said last week no strike would occur until after those contracts expire.
SEPTA spokeswoman Jerri Williams said Wednesday, "We still continue to hope that a work stoppage can be avoided."
The TWU seeks a two-year contract with 5 percent pay raises in each year, while SEPTA is offering a five-year contract with no raises for the first two years followed by annual raises of 1 percent, 2 percent, and 3 percent.
Under SEPTA's offer, workers would get $500 bonuses in 2014 and 2015 and would be required to pay more for their health insurance. The employee contribution would rise from the current 1 percent of salary to 1.5 percent in 2016, 2 percent in 2017, and 2.5 percent in 2018.
New employees would not be eligible for the same pension plan as current workers but would be offered a "457-b" plan, to which the workers could contribute with SEPTA matching up to 10 percent of the contribution.
Brown said SEPTA negotiators appeared to be seeking a contract with terms similar to those recently accepted by city employees represented by AFSCME District Council 47 and state employees represented by AFSCME District Council 13. Those contracts provided average annual raises of about 1 percent.
Brown suggested a better comparison for SEPTA workers would be SEPTA managers, who will get raises of up to 7.5 percent this year, he said.
Williams said that managers' raises, on average, were based on the raises for union workers but that individual managers could get as little as no raise or as much as 5 percent, depending on performance.
The TWU has offered to forgo its right to strike if SEPTA will agree to submit the contract dispute to binding arbitration. SEPTA has declined.
Brown did not predict how soon a strike might occur. He said he expected negotiations to resume this week, and said, "We're going to spend the next few weeks trying to get a deal done."
But Brown said: "We won't go a year or two years or three years without a contract. We're not going to tolerate that."
Brown, who famously said he was "the most hated man in Philadelphia" when he led a six-day transit strike in 2009, said Wednesday, "I'm going to do what I have to do" for transit workers this year.
Typically, the agreement reached by the TWU sets a pattern for the contracts with SEPTA's other unions.
One of those unions represents the engineers who operate Regional Rail trains. They have been without a new contract since 2010, and it's possible they could strike by late this year.
That could raise the prospect of the first-ever shutdown of SEPTA's entire transit system: buses, subways, trolleys, and trains.
Mediation talks between SEPTA and the Brotherhood of Locomotive Engineers and Trainmen in Washington on Tuesday were not productive, according to a union representative, and the engineers are seeking to be released from mediation.
If the two sides are released from federal mediation, that would start a 30-day "cooling off" period and a 240-day dispute-resolution period required before a strike or lockout was permitted.
That period would expire in November or December, depending on when a presidential board was created to investigate the long-running contract dispute.
The engineers last went on strike against SEPTA for 108 days in 1983, after the transit agency took over operation of the Regional Rail system from Conrail.