Please help

I worked for a small company for 5 years, since last year the company started to defer my salary due to some financial problem. I left the company last Dec and so far they still owe me 80% of last year's salary. The owner sent me an email before I left saying that they are going to pay me my salary once they receive the payment from their client but don't know when. Anybody know what action I can take to get my money. Your help are greatly appreciated.