You didn't ask a question, but it is assumed you want to know if this is legal. I will turn the question around: What is the likely outcome if your husband either refuses, or simply does not do it?
Based solely on the information you provided, your husband has not been asked to do anything illegal. If he were asked to do something illegal and he refused, he would have some legal protection. But if he refuses to keep his eye on a co-worker and report mistakes he observes, he runs the risk of being disciplined or fired, himself. The question, here, is why does the boss want the co-worker watched? And what, exactly, is your husband being asked to do? If he believes there are some questionable motives, your husband should talk to an employment law attorney so learn about his rights and obligations under the law.
They say you get what you pay for, and this response is free, so take it for what it is worth. This is my opinion based on very limited information. My opinion should not be taken as legal advice. For true advice, we would require a confidential consultation where I would ask you questions and get your complete story. This is a public forum, so remember, nothing here is confidential. Nor am I your attorney. I do not know who you are and you have not hired me to provide any legal service. To do so would require us to meet and sign written retainer agreement. My responses are intended for general information only.
While it sounds like your husbands employer is delegating its own management duties to your husband, it has the legal right to do so. I agree with the other comment that your husband is not being asked to violate the law, at least not as is apparent from your questions, and that there may be adverse employment consequences if your husband refuses. It's a lousy situation, to be sure, but employers hire employees for their benefit, not for the employees' benefit. Your husband can explain his discomfort or why he thinks he is not the best person to do this task, but don't expect the employer to be sympathetic. There is a reason the employer picked your husband for the job. And if your husband refuses or does a poor job, the employer may see him as disloyal or not a team player . . . not how any employee wants to be viewed when it comes times for raises, bonuses or promotions.
I agree this is a crummy situation. Unfortunately, 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 in California 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 people can do to improve their employment rights is vote for candidates with 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 a union already in place.
twitter.com/MikaSpencer *** 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 the co-worker was obviously a member of a protected class; including the immutable characterisitc of age, race, gender, disabilty, religion, sexuality, etc, I would be tempted to protest that the "spying" seemed to derive from an improper motive and engage HR in the conversation.
But, this idea has obvious and serious hazards, .... and an entirely different way to look at it is perhaps your husband is being asked to demonstrate whether he has managerial skills to evaluate a co-worker's skills. Maybe your husband should be flattered. .
So, perhaps your husband should sit down with employment coach or attorney and get some clarity around what he's being asked to do, and how he wants to respond. .
THIS IS A GENERAL ANSWER TO A GENERAL QUESTION AND SHOULD NOT BE RELIED UPON AS A FULL LEGAL ANALYSIS OF ANY FACTUAL MATTER. An attorney-client relationship is not established or offered solely as a result of this answer.