Bush has been trying to reorganize the INS and the Border Patrol under the Homeland Security Agency, but as you well know, Little Tommy Boy has been stamping his feet and obstructing the bill in the Senate.
That's the problem. Reorganization will only make sure more people are added to the problem, or (at best) shuffle people around. He doesn't need to centralize these agencies in order to take away unionization. If anything, it will make it harder to get around unionization.
Haven't read that part of the bill, so I could be wrong.