How to get my owed salary back

I left my previous company one and half month ago. Before I left, the company owed me almost two pay periods plus around $1,500 traveling expenses. I emailed the company several times but never got answers. Does anyone knows how I can get my money back? Should I report to the local Labor Department? Should I hire an attorney?

Some other related background information: The company is my Green Card sponsor company. In this March, I decided to leave the company because we only get four paid days a week (The boss said he welcomed people to work five days). It is a small company with 6 people, including me. At that time, I submitted my I-140 and I-485 simutaneously in November 2004. I did not see any hope of getting my I-140 approved because the company's financial condition was so bad that not a single financial company would like to give credits to the company. Everyone got owed by one and a half payments. I got a new offer soon and told my boss the I was leaving in two weeks. He said OK. But in the coming weekend, I received a notice from USCIS, notifying that my I-140 was approved (I never expected that the center process my application that fast). I checked the website and found that my 485 had to be suspended for more than 180 days before I changed to a similar job with my Green Card appilcation still being able to continue. After discussion with my collegue, who is also a Chinese, she told me to stay until the 180 days passed (which is mid-May). So I talked to my Boss and asked to extend my stay. As an exchange, I would work five days a week yet got four days payment. He said OK. Then days passed and the final Friday which was a pay day, none did not get any payment and my boss said he would try to work things out. I sent out several emails thereafter but never heard back from the old company. Since I still kept contact with my workmates, I knew they already got 80% of their owed money back. I then thought it to be unfair and would like to ask the suggestion from your friends online.

Btw, there are still several guys who left the company either shortly or two years ago, and they all got owed by the company but the amount were far less than mine. So most of them chose to stay silent but they would like to be witness if being asked.