Four unions sued to halt a bid for Frontier Holdings.

In a suit filed in federal court in Denver, a coalition of four of Frontier Airlines’ five unions charged that a tender offer by Texas Air Corp. for Frontier Holdings, parent of Frontier Airlines, is anti-competitive. In addition, the suit alleged that Texas Air’s real purpose is not to acquire Frontier but to hinder its operations. Texas Air is attempting to buy 7 million of Frontier Holdings’ 12.5 million shares outstanding at $20 per share.