If you want a thorough review to decide if you have a case for unpaid wages, you need to see an attorney who regularly handles those cases. A response on Avvo does not constitute a legal opinion. Also, most labor lawyers and employment lawyers will give you a free consultation to evaluate your facts and documentation. If you have a good case, they will normally take the case without an upfront fee, since fees are part of the claim against an employer who does not pay proper wages. Try Avvo's "find a lawyer" tab for a lawyer in your area who handles these cases.
Questions that your posting don't answer but cry out for an attorney who has experience: (a) Is the waiver valid? (b) What is included in the waiver and what is not? (c) Does this waiver prohibit you from filing in State Court? What about the Labor Commissioner? (d) How much money is the difference that is at issue if you should have been paid wages?
Robert Stempler (please see DISCLAIMER below)
NOTICE: The above statements are provided for general information purposes only and are not intended as legal advice or advice of any sort for a specific case or legal matter. If you do not have a signed attorney-client fee agreement with the Consumer Law Office of Robert Stempler, APC ("the Firm"), then until such written fee agreement is provided and signed by both a prospective client and attorney for a particular case, neither Mr. Stempler nor the Firm will represent you nor will they be your attorney in any matter and you remain responsible for retaining your own attorney and for compliance with any and all deadlines and for any statutes of limitations that may pertain to potential claims. Comments made on a public forum, such as Avvo.com, to not have any confidentiality because others may read them. If you desire a private consultation with Mr. Stempler that is confidential, please go to www.StopCollectionLawsuits.com and submit a free eCase Review. The result portrayed for a client was dependent on the facts of that case. Results will differ if based on different facts. The Firm and Mr. Stempler are a debt relief agency. The Firm and Mr. Stempler help people file for bankruptcy relief under the Bankruptcy Code.
The general answer to your general question is that if your severance agreement contained an enforceable general release of all claims, and you signed the agreement and took the severance payment, and the payment was "new money" meaning not money already owed to you at the time of the agreement, then it is likely you have released the company of any an all claims you have for additional compensation.
If you believe you have a significant claim for overtime, it might make sense for you to have an attorney review the severance agreement to see if there are any ways to undue it. If you think that is where you want to go, you should locate and consult with an experienced employment law attorney as soon as possible to explore your facts and determine your options. I would suggest you look either on this site in the Find a Lawyer section, or go to www.cela.org, the home page for the California Employment Lawyers Association, an organization whose members are dedicated to the representation of employees against their employers.
Good luck to you.
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In the U.S. Eleventh Circuit, where I practice, no agreement resolving an overtime claim under the FLSA is valid unless approved by the Court or the U.S. Department of Labor. You may wish to contact an attorney who specializes in wage and hour claims in California and determine whether the Courts in California have a similar requirement. Good luck.