Local 22 of the International Association of Fire Fighters told Common Pleas Judge Gary DiVito that the elimination of five fire engines and two ladder trucks will endanger lives.
The union wants an injunction so that a grievance on workplace-safety issues, filed with the city on Dec. 3, can be considered before the scheduled reductions.
DiVito plans to resume the hearing on the injunction this afternoon.
The union also asked the Supreme Court to intervene. That court on Monday agreed to hear, in March, Local 22's appeal of a 2007 Commonwealth Court ruling striking from the union's 2005 contract a procedure on how fire companies are closed.
That procedure called for an independent study of fire company closings and city negotiation with the union before they happen.