That said, there are significant exceptions to the rule. You can't discriminate against employees for reasons of race, creed, color, national origin, gender or disability--to name a few classifications. Nor can the company set a policy (for example, as in an employee handbook) and then violate that policy without giving employees notice that the policy has been changed.
Whether or not the lesser severance package was legal in your case depends on a number of factors including:
* The extent to which severance pay was enshrined in policy.
* Whether there were any policies about discounting severance because of disability.
* Where you live and work.
* The number of employees in your company (which determines whether federal or state discrimination laws apply).
* The length of the term of disability of the other employees.
* Whether you had a written agreement with the company outlining these issues.
Because state and local laws can vary, speak to an employee-side (as opposed to "management-side") employment attorney in your area so that you can get specific guidance on your situation.