Negotiations between union truck drivers and the Seattle area’s two major garbage haulers will reach a critical juncture at midnight, according to union organizers. That’s the deadline union officials have set for reaching a contract agreement with Waste Management Inc. and the Rabanco division of Allied Waste Industries Inc. Without such an agreement, the city’s 600 garbage truck drivers could begin striking as early as tomorrow.

Officials from both sides, quoted in published reports during the course of the week, seem optimistic that an agreement can be reached and the strike averted. But as the deadline nears, the parties involved have grown increasingly agitated. The drivers, who are members of Teamsters Local 174, are dissatisfied with rising health care costs and mandatory overtime requirements.

In the event of a strike, the companies say they plan to use replacement workers from other states. However, Theresa Jennings, director of King County’s solid waste division, said garbage service could still be interrupted for as long as five to six weeks.