An organization has a staffing strategy in which it hires 10% more employees than it actually needs in any job category in order to ensure its hiring needs are met

While it's totally normal to recruit and staff certain positions of a company giving room for some slack, this strategy has to be originated from the statistical analysis of desertion in the following months after hiring. Companies are at the strong end of the recruiting negotiation process and this comes with some ethical and legal responsibilities.

In this case, while it is also frequent that after going through an interview process and accepting the conditions of the position, new hires can decline the job almost on any basis, this is not a practice that can be copied by employers. On ethical grounds, it's considered bad behavior offering some conditions and then denying them to meet a number of hires quota. On legal grounds, it can also fall under false advertisement and hurt the company's image, reputation, and credibility.