You really don't have any options here. If you knew of the pay decrease when you accepted the position, then that's what you agreed to. This is true regardless of any prior salary attached to that job. Things would be different if you accepted the position and had a signed employment contract or union agreement stating just what you would be paid. Also, if you worked and retroactively your employer tried to decrease your wages. Both of these instances would be illegal.However, as it stands now you are being paid the salary that you agreed to in advance of commencing employment. You were.are free to stop working there.