Employers have in fact lobbied hard for laws that make this possible in the first place. They want all the benefits of at will employment, so there's no reason why they shouldn't also be on the receiving end of it.
It just means that there's an initial probationary period where the employment is at-will, and beyond that point the employer must have a reasonable cause to terminate the employee. I'm not at all familiar with Montana labor laws in practice, but I find it very difficult to believe that it makes much of a difference.
