"All monopolies are prejudicial to freedom, but there is good reason for supposing that labour monopolies are more dangerous than any others, and that a society in the grip of such monopolies would enjoy less freedom than any other sort of society. In the first place, labour monopolies have shown themselves more capable than enterprise monopolies of attaining really great power, economic, political and even military. Their appetite for power is insatiable and, producing nothing, they encounter none of the productional diseconomies of undue size. Once grown large, they are exceedingly difficult to dissipate and impossible to control. Appearing to spring from the lawful exercise of the right of voluntary association (though as monopolistic associations they are really a denial of that right), they win legal immunities and they enjoy popular support however scandalous their activity. Enterprise monopolies, on the other hand (not less to be deplored by the libertarian), are less dangerous because they are less powerful. They are precariously held together, they are unpopular and they are highly sensitive to legal control. Taken separately, there is no question which of the two kinds of monopoly is the more subversive of freedom. But in addition to its great power, the labour monopoly is dangerous because it demands enterprise monopoly as its complement. There is a disastrous identity of interest between the two kinds of monopoly; each tends to foster and to strengthen the other, fighting together to maximize join extractions from the public while also fighting each other over the division of the spoils. Indeed, the conflict of capital and labour (the struggle over the division of earnings) is merely a sham fight (often costing the public more than the participants) concealing the substantial conflict between the producer (enterprise and labour, both organized monopolistically) and the consumer."
-- from "The Political Economy of Freedom" by Michael Oakeshott: