Taxes and withholding on unpaid salary
As others have said, make sure you can and do file your taxes on a cash basis (not accrual). It sounds like it's very unlikely the company is going to issue you a 1099 for invoices they never paid you. So you just file last year's taxes based on your income, which is the money you actually received. If they do pay you later, in the new year, you'll include that income on next year's tax return, and you would expect a 1099 at that time. Side note: not getting paid is unfortunately common for consultants and contractors. Take the first unpaid invoice and sue them in small claims court. After you win (and collect!), tell them you'll sue them for each unpaid invoice in turn until they pay you in full. (You might need to break up the lawsuits like that to remain under the small claims limit.)