One good reason to have new employees serve a probationary period is that it gives you more time to check their backgrounds and find out whether they were forthcoming on their applications. Then, if you find out someone lied, you can dismiss him or her even if you might not dismiss an established employee for the same omission.
Courts like to compare how you discipline members of a protected class and other employees, but are willing to give you more leeway with a probationary employee. To prove prejudice, the new employee has to show you treated him or her worse than other probationary employees—not every employee.
Recent case: Ihab Elgabi, of Egyptian national origin, applied for a job as a bus driver with a transit company, and authorized a for criminal convictions. On the application, Elgabi acknowledged that he would be a probationary employee for the first 90 days. His background check came back negative.
Elgabi also had applied for a job as a driver with a school district and authorized an FBI background check. The FBI found that Elgabi had a domestic-violence and firearm conviction. When the transit company found out, it fired him.
The news media got hold of the story and ran on all transit employees. It then informed the transit company that 18 of its drivers had criminal convictions. However, only four of them had lied on their applications. Because it couldn’t practically fire all 18, the company selected those who had lied. Two were reinstated after union grievances. None were probationary employees.
Elgabi sued, alleging national-origin discrimination, but the 6th Circuit Court of Appeals tossed out his case. It reasoned that the transit company could legitimately treat probationary employees differently. (Elgabi v. Toledo Area Regional Transit Authority, No. 06-3905, 6th Cir., 2007)