sounds like they are breaching a confidentiality agreement between the employer and the employee
...actually Morno, you will find that this does not have to be explicitly stated in the contract of employment. By common law an employee owes a fiduciary duty to his employer.
"An employee who is privvy to trade secrets of his or her employer will be in breach of the duty of confidence if he or she discloses confidential information during the course of employment to some interested third party."
--Evans M, Equity & Trusts