OAKLAND, California (AP) — With a Sunday night deadline approaching, negotiations between the San Francisco Bay Area Rapid Transit and two of its largest unions have intensified with a possible strike at stake.

As the parties went back to the bargaining table Saturday in Oakland for anticipated around-the-clock sessions, both sides described the talks as tense and said they're far apart on key sticking points including salary, pensions, health care and safety.

About 400,000 riders use BART, America's fifth largest rail system, on weekdays. A strike that could start as early as Monday would be chaotic for those commuters and affect every mode of transportation, clogging highways and bridges throughout the Bay Area.

BART said it has agreed to at least a handful of minor proposals from members of the Service Employees International Union (SEIU), Local 1021 and the Amalgamated Transit Union (ATU), Local 1555, but not on the major issues.

The unions want a 5 percent annual raise over the next three years. Currently, train operators and station agents are paid in the low $60,000 range. Employees average $16,590 in overtime annually and pay a flat $92 monthly fee for health insurance.

Meanwhile, BART has offered a 1 percent raise annually over the next four years and for employees to contribute to their pensions.

The unions' current contract expires at midnight Sunday. On Friday, the ATU asked California Gov. Jerry Brown to issue a 60-day "cooling off" period if no deal can be reached by Sunday's deadline, but the SEIU and BART officials have urged Brown not to issue such an order.

The governor's office has declined to comment.

BART's last strike lasted six days in 1997. On Friday, other area transit agencies urged commuters to consider carpooling, taking buses or ferries, working from home and, if they must drive to work, to leave earlier or even later than usual.