Depending on just how big the unpaid invoice is, in some states small-claims court is an option; it's cheaper and quicker usually. Here's a list of each state's limits for a small-claims-court suit: http://www.nolo.com/legal-encyclopedia/article-30031.html
This a route I took last year for a client. I self represented and the clerks at the courthouse were friendly and helped where they could. In North Carolina, the cap for small claims action is $5000. Once my case was heard, it took 10 minutes between the start and a judgement in my favor. From start to finish though it took two months so as to serve a summons properly and allow time to appeal the judgement.
It helps if you've received checks from the company previously and can give the bank account information to a sheriff to collect for you.
It helps if you've received checks from the company previously and can give the bank account information to a sheriff to collect for you.