BART said earlier this week that its "best and final proposal" included the wage raises as well as increases in pensions and medical coverage.
The BART board would take the whole package -- "because we do not have agreement on the salary increases," she said -- to binding arbitration. The unions seek "20% plus salary increases," she said.
"The issues that remain unresolved are not minor. We cannot get tired and give up. They get to the heart of BART's need to function efficiently and economically," the BART general manager said.
Castelli apologized to the area's commuters.
"We're very sorry. We understand that this strike -- what it does to the Bay Area riders, and we understand that it is a hardship. ... We apologize," he said. "We urge the public to contact the BART district and tell them to finish negotiating a fair deal with our union."
BART workers also went on strike in the summer, paralyzing the San Francisco regional transportation system for four days in July.