is it legal for your boss to put a camera in your office

Yes.

My understanding is that employment law is generally a state matter in the area of privacy issues with private employers. I am not a lawyer and this is not legal advice because specific facts and circumstances will play a big part in whether it is allowed or not. A lawyer in your state would probably answer this question for you quickly and perhaps in an initial consult for no charge.

My understanding is that surreptitious videotaping of employees is generally legal although it may not be in good taste or enhance employee morale. Consent of the employee is not required if there is no audio. If there is also surreptitious audio taping consent of all parties may be required in some states. Consent could possibly be assumed by a stated company policy that is distributed or available to employees.

The Minnesota Supreme Court once remarked, "The idea of surveillance seems distasteful and it may be ill-advised, but that is not to say it would be illegal." Nordling v. NSP, 478 N.W.2d 498 (Minn. 1991). Generally, however, where a legitimate business reason exists, and the surveillance is narrowly tailored to that purpose, courts have not declared an invasion into the employee's privacy. Protection against theft, quality monitoring, etc. are clearly legitimate interests and will not be found to be invasions of employee privacy. If the surveillance occurs in places where the employee has a strong privacy interest, such as a bathroom or changing area, the courts are more likely to find violations of privacy.

Surveillance of employees engaged in union organizing activities is prohibited. Consolidated S & Co. v. N.L.R.B., 305 U.S. 197 (1938). With the narrowing in recent years of privacy expectations by the current court and the lessening strength of unions this rule could be overturned if it were challenged, so I wouldn't count on it. Better to organize elsewhere besides on company property. The employer may surveil non-employee union organizers on the employer's premises. Oakwood Hospital v. N.L.R.B., 983 F.2d 698 (6th Cir. 1993). Collective bargaining agreements should address the issue of employer's monitoring and surveillance of employees in union settings.