There are some skilled trades that companies, even during a recession, can't get around...fire alarm/suppression system inspectors/technicians, elevator inspectors/technicians, electricians, electrical code specialists, OSHA compliance specialists, etc...
You can get around those by not building. New construction is a considerable portion of work in these trades. My family owns a construction company and my father is an electrician. They have three times as many employees in installations as they do service.