I wonder IF this is Legal ?

(In this specific scenario that you're speaking of) With your own authority, you just call them up & ask them if they have a load for you to haul. They may have & they may not have. You can contract with them on a per load basis & run under your own authority. However, Normally an O/O with his own authority trying to get in on a companies loads that already has O/O's leased to them, usually gets the leftovers. Normally a company takes care of the guys who are leased to them first... everybody else gets scraps. When business gets slow, you're the one thats not going to get loads. The leased guys will get the loads if there are loads to get.

My bottom line to my point is, you're barking up the wrong tree. This is not usually a viable business move. It's legal, Its just not a good option. Friends, buddies, co-workers, family... whatever, its just not a good way to do business.