also crack-down, "legal or disciplinary severity," 1935, from the verbal phrase (1915), from crack (v.) + down (adv.); perhaps from crack (v.) in the sense of "to shoot at (by 1913), or from the figurative notion in crack the whip.
These scab contractors probably think that they have us whipped, but they are badly mistaken. With the reorganization of the Building Trades Council, which is progressing nicely, we will be in a position to cope with them and when we do crack down on them they will have to come across or get out. [Journal of Electrical Workers and Operators, September 1915]