I was recently terminated from my job, but I was not notified and had no prior write ups.

I was recently terminated from my job, but I was not notified and had no prior write ups. The job is at a hotel and the way I found out was because I tried to use my hotel discount and my employee number didn't work anymore. I emailed my manager regarding this and she responded by saying they filled my position due to me not having enough availability, this is how I found out I was no longer employed there. It is an on call position, and there are other employees that work once a month or once every few months. I was working 4-6 times a month minimum, nonetheless there was no hour requirement when I was hired.

Is this legal? To be terminated without notification/prior write-ups. I am located in Massachusetts.