i am a truck diver that is covered under the federal labor code because the company that i work for does international boarder crossing, although the company owner does not himself realize this. Our normal work week is Monday to Friday and is usually between 58-65 hours worked. 99.9% of the time home every day , normal work day hours start between 4:00 am and 6:00 am and finish 4:00 pm to 6:30 pm but can be as late as 8:30 pm. i am the most senior driver 7 years and I myself get paid salary because of a verbal deal with the owner made over two years ago.Getting to the problem, normally if there would be Saturday work a phone call would come just after lunch and the request " could you work Saturday?" . I would reply by say no i cant i have something that has to be done or plans or i would reply yes i can . This past year since May 2016 i was asked 4 or five times and said no only once . Until this Saturday past i got the call at 4:00 pm and what he said was that one of our outside carriers and my self was working Saturday he never asked just said i was working . I told him that I couldn't because i had arrangements made to get exhaust work done on my personal vehicle so i could get an E-test and then had to go get an E-test so i could get my sticker for my renewal. he argued with me and I told him i was sorry but i couldn't then he hung up on me. I did not work. I haven't heard anything yet . I am just trying to get my ducks in a row here just in case he tries to terminate me . Is this just cause for dismissal ?