An act done by a person in contemplation or furtherance of a trade dispute shall not be actionable on the ground only that -
(a) it induces some other person to break a contract of employment, or
(b) it consists of a threat by a person to induce some other person to break a contract of employment or a threat by a person to break his own contract of employment, or
(c) it is an interference with the trade, business, or employment of some other person, or with the right of some other person to dispose of his capital or his labour as he wills.