That's a very surprising policy change. Not many years ago contractors at my terminal were not permitted to take package handlers and put them in trucks after the sort and go and deliver. Likewise X was at the time training drivers but we had a multi route with a turnover so extreme that he kept robbing x of the temps they had trained. Finally reached the point where X told him to get his own drivers. Now with the temps being eliminated X has no reason to train anymore. I don't know what some contractors are going to do come peak. Many will no doubt be completely unprepared. If you have to train your own while other's in your terminal don't no question they will be trying to steal them because they won't spend the money,instead expecting you to bear the cost .
When you hire a driver, make them sign a legally binding agreement that they won't go to work for another contractor for at least 1 year., since you are literally in competition with every ISP a non-compete clause makes perfect sense. Figure your cost of training, and sue if they go to another contractor.