Polygraph dragnets of this kind are not without precedent. For example, the Jefferson County, Colorado Sheriff's Department was contemplating such a dragnet in an attempt to find out who released crime scene photos from Columbine High School to the press.

The 1988 Employee Polygraph Protection Act provides no protection to public employees, so unless your state or local government has some law or regulation that would restrict such practices, then your employer might resort to a polygraph dragnet.