Wala pong case na pwede i-file sa mga private companies na hindi nag iissue ng contract sa mga employees nila. A contract of employment can either be written or verbal, both are binding and are laws between the parties. What you should do if you want a written contract is to ask for one or draft one yourself with the stipulation of both parties and ask your employee to sign it.
Pag sinisigawan at minumura ka, pwede yan pumasok sa oral defamation. Not a labor case but a criminal one.