If you are representing clients dealing with workplace privacy issues, you may be interested in Lisa Smith-Butler's article, Workplace Privacy:  We'll Be Watching You, 35 Ohio N.U. L. Rev. 53 (2009). 

For those representing an employee who "believes an employer has gone too far and invaded his or her privacy," the article provides a checklist. While the list neglects to include some of the sources of law mentioned in the article, such as the National Labor Relations Act or a collective bargaining agreement, and could be added to, with for instance state laws similar to the Electronic Communications Privacy Act, it provides a good starting point. 

The article also provides recommendations for best practices which may be helpful to attorneys representing employers.