Different economic theories provide a number of models intended to explain some aspects of collective bargaining:
The so-called monopoly union model (Dunlop, 1944) states that the monopoly union has the power to maximize the wage rate; the firm then chooses the level of employment.
The right-to-manage model, developed by the British school during the 1980s (Nickell), views the labor union and the firm bargaining over the wage rate according to a typical Nash Bargaining Maximin.
The efficient bargaining model (McDonald and Solow, 1981) sees the union and the firm bargaining over both wages and employment (or, more realistically, hours of work).