should we limit the migrant workers head to developed city?

How would you do that? Build huge walls around the city, put patrols around the borders. It will cost a lot of money each month to maintain the city wall. Eventually the people will make holes and come through. You can try to control everyone who enters the city but that's very expensive too. You can make a kind of registry for the companies to note the names of the emplyees that live outside the city and ask taxes for them, but I don't think that's a good idea too. I think it is almost impossible to limit them...