What is the test for an employer to be found guilty of a violation of an employee's rights?

For example, NLRB v. Great Dane Trailers (1967) 388 U.S. 26, 87 S.Ct. 1792, 18 L.Ed.2d 1027 established that some employer conduct is so "inherently destructive" of employee organizational rights as to constitute a prima facie violation which the employer must explain away. Conduct of this kind "carries with it 'unavoidable consequences which the employer not only foresaw but which he must have intended' and thus bears 'its own indicia of intent.' [Citation.]" (P. 33, 87 S.Ct. at p. 1797.)