There was an interesting case that can be a lesson to those employees who try to "right wrongs" through surreptitious means.
Following is a link to the appellate case decision in
Food Lion, Inc. v. Capital Cities/abc, Inc; et al, which centered on undercover reporting by two ABC news reporters trying to document unsafe food handling by becoming Food Lion employees and surreptitiously recording Food Lion activities.
The Court upheld the lower court's decision in favor of Food Lion that the reporters trespassed and breached a duty of loyalty to the company that hired them.
https://law.justia.com/cases/federal/appellate-courts/F3/194/505/505056/
If there is harassment (or any illegal activity suspected) there are better ways to address the problem than by playing detective. Let professionals investigate any claims.