LA's Metropolitan Transit Authority operates most of the county's bus and rail lines. Its contract with unions that represent about 6,800 drivers, mechanics and clerks expired at 12:01 this morning.

Though union officials didn't order a strike, a negotiator said late Monday night that a walkout is still "a very real possibility" if more progress in the contract talks isn't made soon. Unions here traditionally have provided a 72-hour notice before a strike begins.

MTA officials are asking the union to accept a four-day workweek to reduce overtime pay. They also want changes in work rules that sometimes require highly paid mechanics to perform work that can be done by lower-paid employees.

An even bigger issue may be the MTA's plan to contract out more work to other transit companies in an effort to save money. Most union officials are opposed to the plan, fearing that it would hurt their negotiating clout and encourage the hiring of non-union workers.