Yes, in general if you are in the US, ( many countries have a lot of job protection but almost to the point it is hard to discharge bad employee)

Most likely that converstation a month ago was written up as a verbal warning about work not up to standard. Now a written notice of termination.

That was more warning than they most likely had to give you.

In most states unless you have a written contract ( all management should have one) and unless you are part of a uniion ( all non management should be ) then they can just let you go for no reason at all. Perhaps they don't like the color shirts you wear.

They can not fire you for race, religion, sexual preference(i think anyway) and all of the protected reason.

So most likely you had best look for a new job. Sorry