A probationary period allows an employer to evaluate a new employee after hiring him or her, essentially without legal, moral or ethical commitment.
The Federal government often subjects its new-hires to such an evaluation as a condition of employment, by requiring them to work probationary periods for up to one year. Under special circumstances, the Federal government has extended employee probationary periods for up to three years.
Private-sector employers may follow the lead of the nation's largest employer, by requiring their new-hires to work probationary periods too. The typical employee probationary period in the private sector ranges from one to six months.
As indicated, a probationary period allows an employer to evaluate a new employee. However, the underlying agenda is to have the right to fire the new employee without good cause under the Doctrine of Employment at Will.
In other words, often, a new-hire must waive some of his or her employee rights during his or her employment probationary period. For example, besides the fact that an employer likely may justifiably fire a probationary new-hire for any reason, no reason or even an unfair reason under the Doctrine, the employer likely may justifiably deprive the new-hire of benefits too, such as health insurance and sick pay.
An employer may not, however, deprive a probationary employee of benefits required by law. For that matter, an employer does not have the right to break any law, just because an employee is working a probationary period; for example, an employer or its representatives are not entitled to harass a probationary employee—at least not in an illegal, discriminatory way.
Once a new-hire successfully completes his or her employee probationary period, then the employee is entitled to the same rights and benefits that the employer grants to other employees of the same classification.
Should an employer renege on a promise to grant rights and benefits to a new-hire as a reward for successfully completing a probationary period, then the employer might be liable. Such a promise may be explicit or implied; for example, many states consider policy manuals to be enforceable, implied contracts between employers and employees.
Subsequently, if a policy manual promises (so to speak) that an employee is entitled to certain rights and benefits after successfully completing an employment probationary period, then the employer likely must make good on the promise by law. Otherwise, the cheated employee might be entitled to file a lawsuit, which the employer might very well lose. Consult a lawyer for legal advice about that.