Union Pacific Corp.'s Overnite Transportation unit is preparing for a possible strike by the Teamsters this weekend as the trucking industry enters its busiest season. The union has been threatening for several weeks to call a strike "at any time" against the largest U.S. less-than-truckload carrier without a labor agreement. Talks between Overnite--whose California terminals include Los Angeles, Fullerton and San Diego--and the union broke off Sept. 17. The company then rejected a mediation offer from the Federal Mediation and Conciliation Service. The strike is seen as likely to occur this weekend because it's the end of the month, usually a busy time for trucking companies, and the start of the fourth quarter, the industry's busiest because of increased shipments to meet Christmas demand. Overnite expects most of its 12,500 workers to remain on the job. The Richmond, Va.-based company said 1,000 workers from terminals not represented by the union volunteered to work at other facilities during a strike, and has contracted with three companies to provide drivers if needed. It also plans to route freight around terminals where workers are striking. Union Pacific shares rose 75 cents to close at $50 on the New York Stock Exchange.