I am paid one hourly wage for 'day' work and another for 'overnight' work. The problem is that I work many different shifts (e.g. 4pm to 4am or 11pm to 7am, etc.) and until recently have not been given any clarification or consistent application of what constitutes 'overnight' and what constitutes 'day.' My boss has finally decided that if I leave before 2am it is 'day' and after is 'overnight' but told me that this is subject to change at his discretion without notice.
Can he tell me I'm getting a specific per hour wage, then change it without notice? So in his mind I can work all this week thinking that because I'm working until 2am, I'll be paid salary B, but then my paycheck comes and it is Salary A because he changed his mind. Is that legal?