Trade union can also pay a useful role in improving the wages of the workers without causing adverse effects on employment. This case which is intensely associated with the idea of monopsony is of “collusion among employers”. When there are few large firms competing for the same kind of labour they may realize that the increase in the demand for the labour by one firm may raise wages so that all of them have to pay the higher wage rate. If one firm offers a higher wage raise wages workers to itself from the other firms using the same type of labour the others too will have to raise the wage in order to keep the workers with them. Under such circumstances the firms will develop a strong desire to avoid any competition bidding for labour and spoiling the labour market. This may lead to open or tactic agreement among the firms not to raise wages.

But when there is collusion among firms not to raise wages, then the marginal productivity will not be even equalized with the marginal cost of labour. Under collusion among employers, the wage rate will be maintained at customary or agreed level even though the marginal revenue product of labour will stand higher than the wage rate paid. Although the firm can increase its profits by expanding employment to the point where the marginal revenue product equals marginal cost of labour, but in doing so the firm will have to increase the wage rate which is prohibited under collusion.

Under such conditions of collusion, the formation of trade which workers can force the employers to pay the wage rate equal to the marginal revenue product of labour. Such a rise in the wage rate to the level of marginal productivity under pressure of trade union would not create any unemployment, because such a rise in the wage rate will only fill up the gap between the marginal revenue productivity and marginal cost of labour, and will not raise the latter above the former.

Furthermore, even in the case of oligopoly in the product market which is so extensively prevails in the capitalist countries, the increase in the wage rate by the trade union may be achieved without creating unemployment. It is generally believed that the oligopolist confronts a kinked demand curve corresponding to which revenue curve has a discontinuous or broken portion vertically below the kink.