I was ask to come in on my off day but I was not able to can they fairedme because I was not able to come in on my off day.

If you are in an at will state they can fire you without any reason.

It is a iffy situation. If you are union it will depend on a union contract. And it will depend on where you are at.

Normally unless there are other reasons to fire you or other problems, they will issue you warnngs first.

Depends on your company polciy, and weather or not you live in an at will state as scottgem has stated.