You unfortunately cannot order a restraining order against the contractor, but as the previous answerer stated, you will have a case of business slander.
In addition, should he actively and maliciously attempt to interfere with your clients, he would be open for suit under the grounds of "tortuous interference with a business". Any damages and injuries that you could calculate that could be attributed to the contractor would be able to be recovered.
For example, if he would contact your client without being solicited, and by using data recovered or used solely through business relations with you entice them through slander to go to him, and your present contract
with the client is worth $500,000.00, then you would be able to directly attempt to recover $500,000 of lost business, attorney fees, and incidental damages to reputation.
One more thing--if the contractor signed a non-disclosure and confidentiality agreement with you, then he is barred by contract to contact any of your business associates--check your contracts and see if any of your contracts had such clauses. Should he contact them, you may have a fairly simple case of breach to bring to court if he persists. There, you may be able to ask the court to issue an injunction to force the contractor from contacting your clients and business associates.
When he contacts you by 10 am, explain to your contractor that he may be in violation of contractual terms with you, and that you are prepared to go after him should he improperly contact your business associates and clients.
In addition, I strongly suggest you possibly contact an attorney to help you draft your demand letter to him should he not stop, and possibly prepare for litigation. On the bright side, if the courts see your way, they are fairly likely to award attorney fees which should recoup your costs.
Dimitry Alexander Kaplun, Esq.