Yes, an employer in MT, and every other state, is allowed to accept an employee's two week resignation early without allowing the employee to work out their notice. In NO state, including MT, is an employer required to allow an employee who has resigned to work out their notice?
Would you like to know why that is?
I thought you might. I'll tell you.
A few years ago, my then-employer fired an employee for good and sufficient reasons, after plenty of warnings. Unfortunately, they had only just hired me and I hadn't started yet, or I wouldnt' have allowed them to do it this way; they allowed her fifteen minutes to go back to her desk, unescorted, to "say goodbye to people" and gather her personal belongings.
In that fifteen minutes, she:
1.) Deleted several key files
2.) Did $2000 worth of damage to the computer system
3.) Cancelled the travel arrangements for all the senior management for the balance of the calendar year (It was October). We had three offices in three states - those boys and girls travelled a LOT
Can you imagine how much damage an employee who was so inclined could do in two weeks?
You are mistaking the acceptance of a resignation early with a firing.
Two things I am tired of typing: 1.) A wrongful termination does not mean that you were fired for something you didn't do; it means that you were fired for a reason prohibited by law. 2.) The above answer, whatever it is, assumes that no legally binding contract or CBA expressly says otherwise. If it does, the terms of the contract apply.