Should a corporation stop paying its dues or become too obstinate, the Imperial fleets stand ready to remind the wayward company of its obligations. That said, the central empire is far from powerless. The Ministry of Security is involved as well, due to the need for native and/or alien pacification, security forces, defense or surveillance.With this somewhat decentralized setup, a certain level of regional autonomy is inevitable, and the various corporate system governors often cut corners when they can get away with it. In fact, the systems of the colonial diaspora are colonized by the designated Corporations who work hand-in-hand with the Ministry of Investment and Development.
However, the rate of expansion means that the society cannot be ruled that way effectively. The Empire is theoretically under the control of a central monarchy.