Can my salary be docked?

I started to work for small company in January 2010 as a temp. I was hired in May 2010 as a permanent employee. At the time I was told that I would be salary exempt and if I worked overtime I would not be paid. I was given 2 weeks of vacation and 2 sick days. About a year after I started my vacation was reduced to I week and I was told that when the business picked up I would get that week back. Up to August of this year my paycheck was never docked for time that I needed to take off from work for any reason. I was treated as a salaried exempt employee. Then in August they started to dock my salary for time that I needed to take off work for illness and medical testing. When I questioned the docking of my pay, I was told that I since I had taken 3 days of my vacation as vacation, I didn’t have any vacation time left for them to use to cover the time that I needed to take off of work for illness and medical testing. I was told that I should save my vacation time for illness. I asked why this had never been a problem in the past, I was told that they decided that they couldn’t pay for time off because when I am off it is costing the company money. They are not docking my pay but “adjusting it as needed”. Then I was told about how the company was experiencing a cash flow problem even though business has picked up and that they (the owners of the company) haven’t taken a salary in two years and that they had to put their own money into the business. They never thought that I would have a problem with having my pay docked because it is for the good of the company. I was told that they love me and appreciate all the work that I do for them and they don’t know what they would do without me.
I was hired as a receptionist but I do much more. Some of my duties include answering the phone, taking orders over the phone, customer service, entering purchase orders, giving customers pricing, accounts receivable invoicing, freight expediting, creating packing slips for the UPS and FEDEX shipping, filing, doing credit card charges, waiting on walk in customers, taking care of customer pickups and anything else that needs to be done.
Can they dock “adjust” my pay whenever they want to? This is a small company. There are three people in the office plus the owner and his wife (who is in the office probably 1 to 3 hours a week). There is one girl that schedules the UPS and Fed Ex shipping and helps in the production area. Her husband is the warehouse/production manager. Most of the girls in the production area are hired thorough a staffing agency.
I was a salaried employee at several other companies since 2000 and I never had this problem. Can they make their own rules as they go along?
Any help that you can give me will be appreciated.
Pat