Does anyone know what legal right he has to do this? He is President, not King or dictator. Not yet anyway.
All the executive branch agencies do the president's bidding, though it usually less visible than this. One example is the semi-automatic firearm importation "ban" that Bush 41 stuck us with. He didn't even bother with an executive order, he just told the ATF director what he wanted (but at least that *was* already covered by pre-existing legislation, he just told ATF to tighten-up their interpretation of said law).