To me, there is a difference between a protected internal network and posting information on the WWW. Who has access to the internal system? Is it password/firewall protected?
Personally, I would inform applicants/new hires of what will be posted so that it does not come as a shock. I would even add it into an employee handbook if you have one. If the new hire has an issue with it, I would do a little more investigation as to why they do not want their information posted and even give them the reasons that it makes good business sense. For example a person being stalked by an ex-spouse, etc. There will be situations that will deserve an allowance, but not everyone that comes forward.
Certain states have employee privacy laws, but I don't know of any that they would apply to information shared internally for business needs. Certain information is bound by confidentiality laws (ADA, HIPAA, etc). But a lot of employment information is not.
Often when employees bring a complaint and state something is "against the law", I ask them to provide me with a cite to the law they are referencing. Most of the time they can not do so. And since most states are "at will", you could terminate the employee or refuse to hire someone who refuses to allow you to use their information on the internal system, as long as there is no law that protects them for this reason.
Here is one good article I found: http://www.corporatewebsite.com/articles/getting_your_intranet_focused%3A_7_tips_for_effective_personalisation about business needs of an intranet