Sometimes sending a copy of the Complaint you will file if payment is not received within 7 days is sufficient.

 You may also file a complaint with your state's disciplinary board, or whatever regulates attorneys in your state.  Little strikes greater fear in the hearts (we do have hearts) of lawyers that a letter from the disciplinary authority.  

Before you do anything, be sure that the work you did was proper and faultless. A defense commonly asserted to nonpayment is that the work performed was deficient or not timely.