BART management and its labor unions announced that contract negotiations would continue Friday and through the weekend.
A BART strike could potentially begin as early as Monday if the negotiations fail, said President of SEIU 1021 Roxanne Sanchez late Thursday night.
BART management negotiators were briefing the transit agency's directors on the contract talks at their board meeting Thursday morning.
Cecille Isidro, a spokeswoman for Service Employees International Union Local 1021, which represents 1,430 mechanics, custodians and clerical workers, said union leaders hope that BART General Manager Grace Crunican will participate in the contract talks Thursday.
"We need to reach an agreement as soon as possible, and she needs to be at the table," Isidro said.
Crunican previously has said she doesn't need to be at the bargaining table because BART's negotiators know what management's position is.
BART management began negotiating with SEIU Local 1021 and Amalgamated Transit Union Local 1555, which represents 945 station agents, train operators and clerical workers, on April 1.
The workers previously went on strike for four and a half days at the beginning of July but finally agreed to Gov. Jerry Brown's request that
they return to the bargaining table for another 30 days.
When the second round of talks failed, Brown asked for a 60-day cooling-off period, and that period ends at midnight Friday.
Union leaders said Monday evening that they weren't ready to give their customary 72-hour strike notice, but also said they were keeping all of their options on the table, including going on strike.
The notice is a courtesy but is not mandatory.
According to ART spokesman Jim Allison, BART and the unions remain split on issues such as wages and employees' contributions to health care and pension costs.
SEIU Local 1021 and ATU Local 1555 alleged in a joint statement Wednesday night that BART negotiators "pulled the rug from underneath the
unions as well as the entire Bay Area" by withdrawing an offer that had brought the parties close to an agreement.
But Allison said "any suggestion that BART offered a proposal and withdrew it is categorically untrue" and blamed the confusion on "a miscommunication that wasn't on BART's part."