Legally speaking, there are no laws in place that create guidelines for what an employer can ask a previous employer when verifying employment, according to the Monster website. Instead, often times employers have policies that explain the type of information that they can give regarding a current or previous employee, which may or may not protect some of the employee's privacy.
While technically employers can legally ask any question regarding an employee, typically the questions will not go into too much detail, suggests Monster. Instead, some common questions that may be asked include "Why did this employee leave the company?", "Would you rehire this employee?" and "Does this employee cause any sort of threat?".