On November 7, 2006, at 0814 central standard time, an Airbus A-320-200, N428UA, being operated as United Airlines flight 732 collided with a Boeing 737-300, N328UA, being operated as United Airlines flight 672, while taxiing for takeoff at the O'Hare International Airport (ORD), Chicago, Illinois. There were no injuries to the 2 flight crew members, 3 flight attendants, and 110 passengers on board the Boeing, or to the 2 flight crew members, 3 flight attendants, and 96 passengers on board the Airbus. There was substantial damage to the right horizontal stabilizer on the Boeing and minor damage to the left winglet on the Airbus. Both airplanes were operating under 14 CFR Part 121, scheduled passenger service at the time of the accident. Instrument meteorological conditions prevailed and instrument flight rules flight plans were filed for both airplanes. The Boeing was en route to LaGuardia Airport (LGA), New York, New York, and the Airbus was en route to Washington Dulles Airport (IAD), Washington D.C. Both airplanes were taxiing to runway 32L for takeoff. The initial taxi clearance given to both airplanes was Juliet, to Juliet-1, left on Tango to runway 32L with the Airbus following the Boeing. The crew of the Boeing reported they followed the taxi route and turned left onto Juliet-1. While on Juliet-1, they stopped short of the intersecting service road because of traffic in front of them and vehicles on the service road. Because traffic was backing up, the taxi clearance for the Airbus was amended to continue straight on Juliet, to Whiskey, to Tango, then back track on Tango, and hold short of Juliet-1. As the Airbus continued to taxi straight on Juliet it passed behind the Boeing. It was at this time that the left winglet on the Airbus contacted the underside of the right horizontal stabilizer and elevator on the Boeing. Both airplanes subsequently returned to the gates and were deplaned normally.