How do I sue my past employer for wages due when he pays by cash, no paper trail for me to provide?

You can sue your employer for unpaid wages even if his ability to maintain consistent payroll is jeopardized by his cash flow problem. The biggest challenge here is establishing what payments he owes you if you do not have a written contract establishing your hourly wage, how often you get paid, and/or if you are salaried. A court would be able to infer that you were not performing a charitable service or gifting him with your labor. But establishing what you were to be paid and how many hours you put in will have to be established through some other piece of evidence. Do you have time cards or something that indicates how much you are paid per hour? Are you paid per project or by some other unit? Do you have a letter or another document indicating this? The word of a fellow employee may not be sufficient, especially if an argument can be made that the fellow employee has seniority or worked more or less hours or worked on different projects. Any distinction that this fellow employee has will make it difficult for you to argue what you should have been paid. The other related issue is establishing a time period. Proof of how often you were to be paid and when was your last pay period is important to establish how much you were owed when you left for new employment. Without some form of documentation, you may not recover all that you are owed. I'd recommend contacting an attorney to review your options. In the future, although it can be difficult to shift the bargaining power the employer inherently possesses, Id recommend requesting a written agreement even if the terms are subject to change and asking for a signed modified agreement if the terms do change based on the employer's cash flow or other circumstances. Another option (which you may want to combine with the aforementioned) is to create a "paystub"/"receipt" each time you are paid so you can note the date and the amount of pay to establish a record.