The Arizona Capitol Times reports:

Following the guidance of a U.S. Supreme
Court justice, Attorney General Tom Horne has threatened to sue an
effectively non-existent federal commission if it doesn’t put Arizona’s
requirement of proof-of-citizenship on federal voter registration forms.  Horne
is giving the U.S. Election Assistance Commission until Aug. 19 to act,
stating in a July 26 letter to the commission’s acting executive
director, Alice Miller, that Louisiana recently got approval to put
requirements specific to the state on the federal forms.

The Supreme Court may have provided Arizona a path to place the state instructions on the federal form by referencing the state request as an alternative means or exercise of enforcing a state’s constitutional power to determine voting qualifications.

The NVRA permits a State to request the EAC to include state specific instructions on the Federal Form, see 42 U. S. C. §1973gg–7(a)(2), and a State may challenge the EAC’s rejection of that request (or failure to act on it) in a suit under the Administrative Procedure Act. That alternative means of enforcing its constitutional power to determine voting qualifications remains open to Arizona here. Should the EAC reject or decline to act on a renewed request, Arizona would have the opportunity to establish in a reviewing court that a mere oath will not suffice to effectuate its citizenship requirement and that the EAC is therefore under a nondiscretionary duty to include Arizona’s concrete-evidence requirement on the Federal Form. Pp. 13–17

and here:

Arizona might also assert (as it has argued here) that it would be arbitrary for the EAC to refuse to include Arizona’s instruction when it has accepted a similar instruction requested by Louisiana.