Beyond national jurisdiction, the deep seabed and its mineral resources are designated as the ‘common heritage of mankind’. Nevertheless, the governing legal framework does not only consist of international instruments, as domestic legislation issued by sponsoring States also plays a decisive role. The legitimacy of certain national provisions can be questioned though, taking into account the duty to carry out activities in the Area for the benefit of mankind as a whole. For instance, can a sponsoring state demand that the proposed mining activities are in the public interest of the State? Are they allowed to generate revenue by introducing a recovery fee or other taxes? Should developing States enjoy more leeway, given the particular consideration for their interests and needs in the Law of the Sea Convention? This article analyses to what extent creeping national interests in domestic legislation on deep sea mining are in accordance with international law.