Blackmail

I live in Illinois, and work for 3 th shift, 12:00 AM to 6:00 AM. My duty is to perform inspection. My boss wants me to come for 1:00 PM meetings with customer, and this is not first time (3 times this month). I simply can't do it, beacuse of other arrangments. He just left 4 messages on my answering machine, if I don't make it for 1:00 PM, I have to resign, or I'll be fired. Is this legal? I'm never late for work, or if I can't make it ( once in 6-7 weeks), I always call day before. There wear never any other complains, so... any advise, how to handle?

Thanks.

Yes, it is legal, and it is not remotely blackmail. The fact that you work third shift does not excuse you from attending mandatory meetings during other times of the day. Depending on whether you are exempt or non-exempt, you MIGHT have to be paid for that time, but there would be nothing even remotely illegal about firing you for refusing to attend.

How to handle? Either find some way to attend the meeting, or start dusting off your resume.