Most employers have a confidentiality policy that is distributed to all employees. Most of those policies broadly define confidential information. But if your policy defines confidential information to include employee wages and salaries is it legal?
A confidentiality policy that prohibits employees from discussing wages, salaries or other terms and conditions of employment is illegal because it violates the National Labor Relations Act (NLRA). This fact was reinforced in a recent ruling against Aerotek Inc. after two of its recruiters in Nebraska told several employees they were not allowed to disucss their wages as a condition of employment.
Employers need to make sure that their confidentiality policy gives specific examples of what constitutes confidential information, such as business plans and profit margins, and does not prohibit employees from discussing their wages, salaries, working conditions or other terms and conditions of employment.
Tennessee Employment Law 
Is there a citation to this ruling? I am very interested in reading this as I review Employee handbooks from time to time.
Thanks for the question. There are several NLRB opinions which address this issue. You can find them on the NLRB website, http://www.nlrb.gov.
Chad