My employer hired me and paid me a salary. After 90 days they want me to become a contractor. They are trying to get me to repay the money I received as an employee from the commissions I will earn as a contractor. Is this legal?

I was hired on February 12, 2018 and was given a salary of $55,000 per year and in 90 days we would evaluate my performance and they would want me to become an independent contractor. About a week ago, we all sat down and they told me that starting June 1st I would go on straight commission as a contractor. I would receive a draw of $4000 per month that would be deducted from my commissions. I understood that under salary I would receive no commissions on the sales during that period. Now they are telling me that once I go on commission, I will have to repay all the salary they paid me, as well as any draws before I will receive commission. Why do I have to repay my salary? I was an employee.