Under WA state employment laws can an employer reduce an employee's salary

Employer reducing employess's established salary: I work for a large health care center in Seattle. I have worked here for 10 years. I started here with a master's degree. At that time, there was no position to compensate an employee with a master's. So presumbaly I was caterogorized as a supervisor, even though I did not really function as a supervisor, to compesnate for the master's. Within the last year the company has been going through changes, growing etc. It has been alluded by administration to me that since I have the supervisor title, I will need to assume new duties involving a supervisory role. It was presented to me that if I did not accept the supervisor position that "my salary would need to be looked at". This seems a bit threatening. My question, can a employer reduce a employee's established salary? - Is this your question? Add additional information