Department of Justice also needs to approve the acquisition. Unlike the heavily contested AT&T proposal to purchase T-Mobile, which the DOJ fought tooth and nail to prevent, the Softbank acquisition doesn't remove a major U.S. carrier from the scene. As a result, most observers expect no objection from the FCC and DOJ to Softbank's acquisition of the vast majority of Sprint. In addition, with over 25% of the company changing hands, Sprint needs a declaratory ruling to close the deal. Softbank plans on making a capital injection of $8 billion which Sprint will use to help build out its LTE network.
Before AT&T eventually decided not to pursue the T-Mobile acquisition, the biggest critic of the deal was Sprint and its CEO Dan Hesse. Whether it is revenge or not, AT&T seems to be the largest naysayer regarding Softbank's acquisition of Sprint, saying that the Japanese firm will have control over too much spectrum if the deal is allowed to close.
source: Reuters via Phonescoop