I am a California attorney and cannot give legal advice in your state. My comments are information only, based on federal law and general legal principles. YOUR STATE MAY HAVE ITS OWN LAWS THAT OFFER SIMILAR OR GREATER PROTECTION. If I mention your state’s laws, it only means I did a quick Internet search and found something that looked relevant. You MUST check with an attorney licensed in your state to learn your rights.
You asked what your best course of action is. That's easy. Consult with an experienced plaintiffs employment attorney with whom you can go over the details and explore options. Employment law is complicated and fact-specific. You may wish to consult with an experienced plaintiffs employment lawyer, and any response to your situation will turn on specific facts. The Avvo board is not set up to handle the kind of detailed analysis needed to offer helpful guidance. Avvo works best for short, specific questions that allow for short, specific answers. Perhaps more importantly, anyone can read the discussions on Avvo so they are not confidential. The employer or whomever is involved in the dispute can read everything written here.
You should know in advance that employees and job applicants have very few employment rights, and employers have a lot of leeway in how they choose to run their businesses. In general, an employer can be unfair, obnoxious or bad at management. And an employer can make decisions based on faulty or inaccurate information. An employer has no obligation to warn an employee that he or she is not performing as the employer wants. It’s not a level playing field. An employer hires employees to provide work for its benefit, not for the benefit of the employees. Don't expect the employer to take care of its employees; it doesn’t have to and it rarely does.
There are some limitations on what an employer can do, mostly in the areas of public policy (such as discrimination law or whistle blowing), contract law, union-employer labor relations, and constitutional due process for government employees. Please see my guide to at-will employment which should help you understand employment rights: http://www.avvo.com/legal-guides/ugc/an-overview-of-at-will-employment-all-states. After you take a look at the guide, you may be able to identify actions or behavior that fits one of the categories that allows for legal action. If so, an experienced plaintiffs employment attorney may be helpful.
Employment rights come from the state and federal legislatures. One of the best things working people can do to improve their employment rights is to vote for candidates who have a good record on pro-employee, anti-corporate legislation. Another way to protect employment rights is to form or affiliate with a union, or participate in the union already in place.
I hope you can resolve your situation and wish you the best.
*** All legal actions have time limits, called statutes of limitation. If you miss the deadline for filing your claim, you will lose the opportunity to pursue your case. Please consult with an experienced employment attorney as soon as possible to better preserve your rights. *** Marilynn Mika Spencer provides information on Avvo as a service to the public, primarily when general information may be of assistance. Avvo is not an appropriate forum for an in-depth response or a detailed analysis. These comments are for information only and should not be considered legal advice. Legal advice must pertain to specific, detailed facts. No attorney-client relationship is created based on this information exchange. *** Marilynn Mika Spencer is licensed to practice law before all state and federal courts in California, and can appear before administrative agencies throughout the country. She is eligible to represent clients in other states on a pro hac vice basis. ***
If there is space on the memo, you may try to write a rebuttal on it indicating that this is "the first audit you have received pursuant to the email (dated x)." In addition, you may wish to cross out the term "final" and indicate that this is your "first" warning. Whether or not you will be allowed to do this will be dependent on your employer but you may want to preserve the integrity of the evidence in your employee file. If there is no space to write a rebuttal on the memo, you can state that the memo is not valid without your attached rebuttal above your signature so that future staff and/or human resource staff knows that a second document must be reviewed.
If you are part of a collective bargaining unit, then you may seek the advice of your current union steward. If there are no unions involved, then you may seek to consult with an attorney to get legal advice if you deem the facts to be discriminatory and could result in your ultimate termination of employment. The information you provided is too limited to provide you with legal advice so undergoing a consultation with a knowledgeable attorney of state or federal employment laws is highly recommended.