"The essence of the strike, then, is the resort to coercion to force unwilling exchange or to inhibit willing exchange."

“Rarely challenged is the right to strike. While nearly everyone in the population, including the strikers themselves, will acknowledge the inconvenience and dangers of strikes, few will question the right-to-strike concept....
    "This is not to question the moral right of a worker to quit a job or the right of any number of workers to quit in unison. Quitting is not striking, unless force or the threat of force is used to keep others from filling the jobs vacated. The essence of the strike, then, is the resort to coercion to force unwilling exchange or to inhibit willing exchange. No person, nor any combination of persons, has a moral right to force themselves—at their price—on any employer, or to forcibly preclude his hiring others....
    "Lying deep at the root of the strike is the persistent notion that an employee has a right to continue an engagement once he has begun it, as if the engagement were his own piece of property. The notion is readily exposed as false . . . A job is but an exchange affair, having existence only during the life of the exchange. It ceases to exist the moment either party quits or the contract ends. The right to a job that has been quit is no more valid than the right to a job that has never been held."

~ Leonard Read, from his 1969 The Coming Aristocracy

"Unionism...[utilises] crude doctrines of sheer force, constraint of anybody and everybody who stand in the way of the immediate end, limitation of numbers and excessive prices built up on monopoly. . . 

    "[T]he labour of the country never can obtain for itself, except at the expense of other labour, more than the free and open market will yield. . . . Extracting more . . . is very near to dishonesty, since he is forcing this higher price at the expense of others. . . .
    "If the employer had behaved badly, the true penalty would fall upon him; those who wished to leave his service would do so . . . That would be at once the true penalty and the true remedy. Further than that in labour disputes has no man a right to go. He can throw up his own work, but he has no right to prevent others accepting that work. 

    "Force rests on no moral foundations."

~ Auberon Herbert, composite quote from his his 1891 'The True Line of Deliverance,' and his 1908 'A Plea for Voluntaryism' 

[Hat tip Gary Galles]