We spoke to a number of stakeholders about the possibility of conducting a partial check, but we were told that there was a risk of tension between the employer and employees or a possibility of reprisals. The employer could ask questions and might wonder whether, if we went to see his or her employees, it was because someone had blown the whistle. There is a fear of this.
However, I have thought that a systematic check could eliminate this problem. Perhaps a random check might, at the very least, be a compromise between efficiency and risk...?