BART strike? Unions threaten to cripple San Francisco's morning commute.

BART strike: BART workers unions might go on their second strike in four months, against the nation's fifth biggest commuter line. Workers will walk off the job at midnight if BART officials don't change their mind, said a union official.

Workers threatened on Thursday to halt the San Francisco Bay Area's largest commuter rail line after six months of on-again, off-again negotiations fell apart.

The two largest Bay Area Rapid Transit workers unions said they would walk out at midnight unless management agrees to enter arbitration to resolve remaining issues. It would be the second strike against BART, the nation's fifth biggest commuter line, in four months.

Roxanne Sanchez, president of Service Employees International Union Local 1021, said BART and the unions have "come extremely close" to agreement on economic, health care and pension issues but that the parties were far apart on work rule issues.

She said the unions suggested taking the remaining issues to arbitration but management refused. Workers would walk off the job at midnight unless BART officials change their mind, Sanchez said.

BART General Manager Grace Crunican said the rules that the agency wanted to include in the contract were necessary to help managers run the system efficiently and control costs. She urged the union leaders to let their members vote on management's offer by Oct. 27.

"We hope to continue to work with the unions, but what's critical at this juncture is that the unions take this offer to a vote," Crunican said.

The impasse came after a marathon negotiating session that ran well into a second day Thursday as both sides worked toward a deal to end the contract dispute that has left many riders under the repeated threat of a commute-crippling strike.

A team of federal mediators who participated in the talks for four days said the parties succeeded in agreeing to a number of significant items, but were ultimately "unable to bridge the gap" on the work rules.

"This is a classic example of a labor dispute that has implications far beyond that of the individual parties," George Cohen, who led the team, said. "Unfortunately, regrettably, we were not able to bring home the result we all want to achieve, which is a voluntary collective bargaining agreement."

Hundreds of thousands of commuters have endured seven strike deadlines, sometimes staying up past midnight waiting to hear if the trains will run in the morning. They were left having to find alternative forms of transportation for Friday's commute.

"I don't want to get in my car again," BART rider Kyle Brunnette, 53, of El Cerrito said. "I think the public would have such bad blood this time around for both BART and the unions if there is a strike."

The contentious labor talks between BART and unions have dragged on for six months — a period that has seen a chaotic dayslong strike, a cooling-off period and frazzled commuters wondering if they'll wake up to find the trains aren't running.

BART spokeswoman Alicia Trost said the agency has been flooded with calls and emails this week from commuters frustrated that they haven't been given earlier notices.

About 400,000 riders take BART every weekday on the nation's fifth-largest commuter rail system.

The key issues during most of the talks had been salaries and worker contributions to their health and pension plans.

Talks began in April, three months before the June 30 contract expirations, but both sides were far apart. The unions initially asked for 23.2 percent in raises over three years. BART countered with a four-year contract with 1 percent raises contingent on the agency meeting economic goals.

The unions contended that members made $100 million in concessions when they agreed to a deal in 2009 as BART faced a $310 million deficit. And they said they wanted their members to get their share of a $125 million operating surplus produced through increased ridership.

The unions said one of the work rules that BART wanted to change was employees' fixed work schedules. Mark Mosher, a communications consultant with SEIU Local 1021, said some workers work 4-day, 10-hour shifts while others work 5-day, 8-hour shifts.

"Some want longer work hours and shorter shifts due to child care, for some, it's the only way a two-earner family can organize child care, but BART wants to schedule people whenever they want," Mosher said.

But the transit agency countered that it needed to control costs to help pay for new rail cars and other improvements.

"We are not going to agree to something we can't afford. We have to protect the aging system for our workers and the public," Crunican said.

On Sunday, she presented a "last, best and final offer" that includes an annual 3 percent raise over four years and requires workers to contribute 4 percent toward their pension and 9.5 percent toward medical benefits.

The value of BART's proposal is $57 million, BART spokeswoman Alicia Trost said.

Workers represented by the two unions, including more than 2,300 mechanics, custodians, station agents, train operators and clerical staff, now average about $71,000 in base salary and $11,000 in overtime annually, the transit agency said. BART workers currently pay $92 a month for health care and contribute nothing toward their pensions.