This would apply only to the 15 executive departments — the Secretaries of Agriculture, Commerce, Defense, Education, Energy, Health and Human Services, Homeland Security, Housing and Urban Development, Interior, Labor, State, Transportation, Treasury, and Veterans Affairs, as well as the Attorney General.
Currently those laws (which are technically called “rules”) are interpreted by the agencies themselves, with the reasoning being that the subject matter expertise of those agencies is the most important factor in deciding any dispute relating to any rule. The laws and judicial process works differently when it comes to agencies under the executive branch.
Having an external governing individual is better than self-governance in most systems, so this seems sensible given that those agencies have a history of interpreting rules in ways that are self-interested and clearly not to the spirit of the rules, which likely resulted in this Executive Order.