I am very sorry this is happening to you.
Unfortunately, nothing can be done about the fact that an employee is violating the company's policy with respect to references. That is purely an internal personnel matter for the company. The can discipline and even terminate an employee for violating protocol but you do not have a right to sue the company or any of its employees because an employee there has violated company policy.
The only potential claim here is for defamation. However, defamation claims only arise from false statements of fact, and saying that you don't "work well" with certain employees would likely be construed as a statement of opinion. Statements of opinion are not provable as true or false because they are inherently subjective. As such, they cannot give rise to claims for defamation.
There is a second problem with a defamation claim as well, which is that employers (and the employees working on their behalf) are protected from defamation claims in the context of response to reference requests unless malicious intent can be shown in ADDITION to falsity of the statement. Proving malice is very hard. You would essentially have to demonstrate that this person was trying to block you from getting a new job and that was their sole intent.
Still, a cease and desist letter can be an effective remedy in these circumstances. Just because a legal claim would be unlikely to succeed does not mean a lawsuit still cannot be threatened. Since this employer has little to gain by saying bad things about you and much to potentially lose in legal defense costs if they are sued, a cease and desist letter can often stop an employer from giving a bad reference. That, and making clear that the CEO should be contacted for references in your applications for future employment would typically be your best bets here.
I hope that you find this information helpful. Please do not hesitate to let me know if you have any questions or concerns regarding the above and I will be more than happy to assist you further.
If you do not require any further assistance, please be so kind as to provide a positive rating of my service so that I may receive credit for assisting you. Very best wishes moving forward.
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