OAKLAND -- AC Transit workers on Monday morning issued a 72-hour notice that they would walk off the job on Thursday morning -- a move that, in tandem with an impending BART strike, could leave the second- and third-biggest transit operators in the Bay Area shut down.

AC Transit carries 100,000 people round trip each day and was expected to carry the bulk of the transit riders during a shutdown of BART, which carries 200,000 people round trip each day.

The AC Transit strike threat came as a surprise after the unions and the East Bay bus provider twice came to tentative agreements this summer after their contract expired at the end of June.

An AC Transit bus in August 2013, the morning after management and the union came to an agreement to avert a strike.
An AC Transit bus in August 2013, the morning after management and the union came to an agreement to avert a strike. ( Laura A. Oda/Bay Area News Group)

Bus drivers and other members of the local Amalgamated Transit Union, in a different chapter than the BART ATU local, twice rejected contract agreements. Union president Yvonne Williams said workers are angriest about what she described as management's proposal to increase health care contributions to 10 percent, which would cost $283 a month for some families, she said.

"It's more of a coincidence" that AC Transit would be striking at the same time as BART, said Williams, adding that no contract talks are scheduled this week. "We have not been able to really get a contract in place that the members feel comfortable with."

"We do not take this action lightly," Williams said.

BART union representatives remained in negotiations with management Monday evening, but the talks appeared to be strained, with the unions essentially refusing to entertain the "take-it-or-leave-it" offer management made late Sunday.

Contact Mike Rosenberg at 408-920-5705. Follow him at twitter.com/RosenbergMerc.