The short answer is, probably. The longer answer is that the question requires much more in-depth analysis. Assuming you work for a private employer (i.e., not a governmental body), there is no constitutional protection. As to private employers, the law generally requires a balancing of the employer's legitimate interest (productivity; preventing theft, harassment, etc.; quality control; etc.) with the employee's reasonable expectation of privacy. An employee will have different expectations of privacy (e.g., in the bathroom, outside the office on company business; at her desk; in her purse and personal possessions; etc.), but the expectation of privacy can be greatly reduced by the employer through known policies with respect to surveillance.
Kindly note and remember that my response is merely a general comment on the law related to your question, and NOT legal advice or opinion. Also, your question and my response does NOT create an attorney-client relationship between us. You cannot rely upon what I have written, because I do not have all of the information that I need to advise you or render an opinion. Even simple facts you have not shared can completely change my answer. For me to give you legal advice or opinion, you would need to hire me to be your lawyer, and then we would need to discuss this in detail and go over the documents.
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With best wishes,
Barry F. Gartenberg, Esq.