Does anyone know the law regarding..?

Libel, Slander, Defamation of Character and what employers are supposed to do to protect employees? I recently had two people i work with write this really nasty letter accusing me of saying and doing things that ive not done or said my boss was supposed to take care of it but i got another note last night from another person.. i cannot go into more detail due to the nature of my job but my husband wants to get a lawyer and sue my co-workers and possibly employer if they dont make the harment stop..