The authority to require registration of commercial equipment, but not hobby equipment (and are in fact prohibited from it). If a change is to be made for hobby equipment, it would make more sense to change it to operate like a ham license than try some harebrained registration scheme doomed to failure in both the courts of law AND the court of public opinion...
No, the FAA is actually statutorily required to register all aircraft:
49 U.S. Code § 44101 - Operation of aircraft
(a)
Registration Requirement.— Except as provided in subsection (b) of this section, a person may operate an aircraft only when the aircraft is registered under section
44103 of this title.
In the administrator's logic for requiring the registration of model aircraft, well read it for yourself:
"In 2012, Congress confirmed that UAS, including those used for recreation or hobby purposes, are aircraft consistent with the statutory definition set forth in 49 U.S.C. 40102(a)(6). See Pub. L. 112-95, sec. 331(8), 336 (defining an unmanned aircraft as “an aircraft that is that is operated without the possibility of direct human intervention from within or on the aircraft,” and model aircraft as “an unmanned aircraft that is capable of sustained flight in the atmosphere, flown within visual line of sight of the person operating the aircraft, and flown for hobby or recreational purposes”); see also Administrator v. Pirker, NTSB Order No. EA-5730, (Nov. 17, 2014) (affirming that the statutory definition of aircraft is clear and unambiguous and “includes any air aircraft, manned or unmanned, large or small.”). Because UAS, including model aircraft, are aircraft, they are subject to FAA regulation, including the statutory requirements regarding registration set forth in 49 U.S.C. 44101(a), and further prescribed in regulation at 14 CFR part 47."
The FAA is probably correct that 49 USC §44101(a) does require that all aircraft be registered. More on that below.
But there are there are two things wrong with this statement. First, the court has already told the FAA that section 336 is not to be interpreted as a rule and if the FAA wants to make a rule based on Section 336 they need to go through the rulemaking process. Second, the NTSB Pirker decision said:
"At this stage of the proceeding, however, we decline to address issues beyond the threshold question that produced the decisional order on appeal: Is respondent’s unmanned aircraft system (UAS) an “aircraft” for purposes of § 91.13(a), which prohibits any “person” from “operat[ing] an aircraft in a careless or reckless manner so as to endanger the life or property of another”? We answer that question in the affirmative."
In other words, the Pirker NTSB decision determined that
only 14 CFR §91.13 'Careless and Reckless' is applicable to model aircraft.
Next is the problem of making an emergency rule (SFAR) to implement this registry in less than two months, bypassing the normal NPRM process. 14 CFR §91.139 - 'Emergency air traffic rules' gives the administrator the authority to make up rules "Whenever the Administrator determines that an emergency condition exists, or will exist, ". I am pretty confident that someone will challenge the validity of the emergency rule on the ground that it was issued in violation of the Administrative Procedure Act's (“APA”) notice and comment provision, 5 U.S.C. § 553(c). In other words, 'what emergency'?
If 49 USC §44101(a) does require that all aircraft be registered, the fact that the FAA has never followed the statute with model aircraft for decades, then they had plenty of time to promulgate rules through the normal NTSB process. In other words, what emergency?