I had two permatemp jobs in my career. You are called an “independent contractor” and file your taxes as one so that the employer could skip out on the same wages and benefits that they offer normal employees on top of getting a tax break. Another added bonus for the company is that they could “terminate the contract” at any time leaving you with little to no recourse.
You have to do everything they tell you to, and you have almost no flexibility at all in terms of hours, when/how to bill, when you do your work, etc. If you try to act like a real independent contractor they will throw you out. There are thousands and thousands of permatemps being misclassified, but none have the financial power to go toe to toe with lawyers of corporations.
It is a big problem but I almost see nobody talking about, maybe because it's more commonplace in white collar jobs than blue collar jobs, but plenty of white collar workers are getting shafted too (and this is just one example).