Obviously there are federal regulations that every all ATC towers need to follow, but every airport is also unique. So there are also local procedures: Staffing levels, runway usage, airspace restrictions, noise-abatement procedures, etc. All of that has to be defined for each airport. It wouldn't make sense for LaGuardia to have to follow the same staffing directives as the airport in say, Fargo, ND.I am a little confused here. But it sounds like that this "procedure" is a local, LaGuardia rule, not a federal regulation. Is that right? I think NY Port Authority owns/operates LaGuardia, is it their rule?
Even though this is specific to LaGuardia, it wouldn't be a Port Authority rule. ATC is part of the FAA, while the Port Authority is jointly owned by NY & NJ. The PA would not have any say over how the airport tower is staffed. That's under the FAA's purview.
For what it's worth, here's what the NTSB report that's referenced in the article actually says.
(Note: The NOTICE was dated April 16, 1997 and states in part, "in light of recent events, the following procedures will [be] in effect immediately, and will be incorporated in the LaGuardia tower standard operating procedures order. A. The local and ground control positions shall not be combined prior to 0000. B. All vehicles on active runways will be on the local control frequency. C. Whenever a vehicle is cleared onto an active runway, the "VEHICLE" strip shall be placed in the local control flight strip bay for the affected runway. D. During night operations, when the Port Authority is working on the active runway(s), they will request that the runway edge light be turned off.")
(bolded by me)