What is "work to rule"

alt. (context idiomatic English) To work slowly by strictly following all work rules, usually in a work-to-rule job action, as part of unionized labor protest. n. Such industrial action vb. (context idiomatic English) To work slowly by strictly following all work rules, usually in a work-to-rule job action, as part of unionized labor protest.

n. a job action in which workers cause a slowdown by doing only the minimum amount required by the rules of the workplace