Probably can under national security/clear and present danger doctrine. Court will have to decide.
US Patriot Act: Freedom of speech: The government may prosecute librarians or keepers of any other records if they tell anyone the government subpoenaed information related to a terror investigation. "Anyone"? Does this also include local law enforcement agencies? A clergyman, in confidence?
Probably can, because it is a tortious activity to allow harassment of employee. I think it goes outside of speech law into what an Employer has a duty to do which is to protect employees. EEOC can regulate workplace environment.
Under Title VII of the Civil Rights Act of 1964, employers may sometimes be prosecuted for tolerating "hate speech" by their employees, if that speech contributes to a broader pattern of harassment resulting in a "hostile or offensive working environment" for other employees. Pretty vague, huh?