NOTE: It is possible to freeze access to your employment data here: https://employees.theworknumber.com/employee-data-freeze That being said, it doesn't stop employers from continuing to hand Equifax your data on a gold platter, and therefore does nothing to protect you from the inevitable data breach that will result in Equifax being required to give everyone affected $0.36 or one year of free credit monitoring.
edit: and a past employer that used this system
Birthdays are extremely easy to get (public record), and I seem to recall a specific large organization leaking a bunch of SSN's not too long ago.......