What you should know about your at will employment at IBM
1. Can IBM terminate me without a good reason?
Yes. In fact, most employees in the United States are at-will employees, even though most employees are unaware of this situation. In most states, the law presumes that private sector employees are employed "at-will." The employment-at-will doctrine provides that both the employer and the employee can end the employment relationship at any time without notice or reason. This means the employer has the right to terminate your employment at any time, for any reason, or for no reason at all or for a bad reason, so long as the reason is not illegal - even if your performance has been outstanding.

2. Are there any exceptions to the employment-at-will doctrine?
Yes, there are several exceptions. You are not an at-will employee if you have a contract, such as a union contract. When an employee is covered under an employment contract, you can only be terminated as the contract permits. If the employer does not follow the contract in terminating or disciplining you, you may have a breach of contract claim.
A handbook or personnel code may also be a contract. However, if there is a disclaimer in your handbook, it may not be a contract. State laws vary in evaluating whether a handbook is a contract. You should consult your own state's law to determine if your state considers handbooks to be contracts between employers and employees.
An employee may not be terminated for an illegal reason such as their race, sex, age, religion, nationality, or disability.

- from the Workplace Fairness Website -