In other words, you have no idea why you are being disciplined.
Employers are required to follow their own disciplinary policies, but only if the policies are provided to an employee as part of the offer of continued employment, such that the employee relies on those policies in the performance of the job.
Assuming that your employer has such a policy, and you relied on that policy, and you were disciplined outside of the employer's following the policy, then you would have a claim for breach of contract
against the employer.
If the disciplinary action
has been published, whether in writing or by oral communication, and the reason provided is false, then you would have an action for defamation of character against your employer.
Both of these claims have been affirmed by the Colorado Supreme Court in Churchey v. Adolph Coors Co., 759 P. 2d 1336 (1988).
If you would like to pursue claims against your employer, you will need an employment rights
lawyer. I must be honest with you here, that at this point in time, your damages may be too limited to justify any attorney taking your case on contingency (no upfront fees). It would be different if you were already terminated, or you suffered a demotion in pay, etc.
But, as a pure academic matter, the employer can be subject to liability.
Re your question as to whether or not a particular investigation process is required by law, the answer is, "no." The law leaves it entirely to each employer to decide how to manage and discipline its workforce. The only restriction is that once the employer sets forth a policy in writing, it must follow that policy.
Please let me know if my answer is helpful, or if I can provide further clarification or assistance.
And, thanks for using justanswer.com!