The transit agency serving the Philadelphia area has publicized contingency plans in case of an employee walkout.
The Southeastern Pennsylvania Transportation Authority's contract with transportation workers expires at 12:01 a.m. Saturday.
SEPTA officials said Friday that they've asked the union for a three-month contract extension.
The Transport Workers Union Local 234, which represents about 4,700 employees, said its members will remain on the job while negotiations continue.
"We’re willing to go the extra mile to reach a fair agreement," said Willie Brown, president, TWU Local 234. "We’re not willing to sign on to a lengthy contract extension or make hasty decisions having a long-term effect on our members’ family finances."
If a work stoppage becomes necessary, union officials said it will involve all three TWU bargaining units. Contracts for employees at SEPTA’s Frontier and Red Arrow divisions expire during the first week of April.
The last strike by SEPTA transit workers in 2009 lasted six days.