Charged Extra For Missing Work

I work as a 1099 subcontractor in North Carolina for a company subcontracting under a master contractor. I work 7 days a week with no PTO or benefits, the raw 1099 deal. I have never signed or received a copy of a contract of employment. I've been grinding this out for 3 years now. Things are starting to get iffy, and something occurred to me I'd like some opinions on.

When I take time off, I am charged an additional fee for the day. It's 30 dollars more than I would have made by going in to work. The first time this happened, it was explained that they had to refund the contract for the night and it came out of my pay. However, when I had a person hired on with the company and they clocked in instead of me, I still got charged the fee even though the job wad covered. It was then explained that they have to pay extra for someone to come out to my region and cover it, and it comes out of my pay.

Google says "generally" this is not legal, but I'm not sure if there is more nuance or if it would be worth contacting a lawyer about. One of my primary concerns is if I quit without notice, will I be charged the additional fees and will they take it out of my final paycheck? If it takes them 2 weeks to replace me, could they justify charging me 30 dollars a day for all 14 days? I've never heard of anything like this happening, but it feels like I'm trapped here.