Is it acceptable for an employer to query previous employers/coworkers as to how effective they were in related jobs? Of course. This is called "checking refer

Is it acceptable for an employer to query previous employers/coworkers as to how effective they were in related jobs? Of course. This is called "checking references" and is standard practice that nobody disagrees with. The key words here are "employers/coworkers" and "related jobs", which are distinct from "high school friends" and "church socials".