Told my employer I might be facing a medical co diction and then they reduce my pay

I have been in my current position for 9 months. During these 9 mo this I have worked tremendous hours, and have taken on other responsibilities to help with our company success. My employee was aware that I had a regular checkup last week. On Friday I shared with my employer that I had to meet with a specialist on December 4 and that I had a potential serious blood disorder. The following Wednesday I received a call from the partners, telling me they hire an additional person. This new person has no experience in this position. They said that in order for the company to afford her, they needed to reduce my salary. They want to give me a bigger workload and reduce my salary to her exact offer. (This equates to a 15% workload) I have been loyal, worked excessive hours, fufilled all my job responsibilities and more. They had hired someone before, who was offer the same position with same pay rate, yet they did not reduce my salary. ThT person lasted less than a month. Since that time I have done my job and this other persons job. I believe they have reduced my pay because I shared the potential medical issues that I am facing.