Severance packages are often offered by employers to allow an employer to make a clean break with an employee. But there is a catch. The employer will almost always require the employee to sign a "release of all claims" in exchange for the severance agreement.
This may be simply a formality in some situations, but in others, the employer may actually know it has violated the law and is attempting to insulate itself from liability "on the cheap." Before signing away valuable rights, especially where the employer sets a short deadline for the employee (this "pressure selling" tactic may be a red flag that the employer is up to something), it may be wise to consult an attorney to review the agreement before you.