You are not a bank. You are an employer. You also do not have to pay mileage. They can claim their mileage on their tax return.
I really feel for you. I have a few construction companies, and they are really in a tough spot in this economy. Don't let your employees push you around. You have a business to run. Kindly remind your employees that we are in the middle of a recession and that there are 18 million unemployed people in the country who would love to just have a job.
Tell them a little nicer than I just wrote it, though!