The New Jersey requirement was a special license plate or decal issued to identify petroleum haulers, and both the New York City and Cook County requirements were for decals connected with local taxation.
According to ATA's State Laws Newsletter, the association based its challenges on a federal statute, 49 U.S.C. 14506, a part of the 2005 federal highway reauthorization, which prohibits all state and local identification requirements for interstate motor carrier vehicles, apart from certain narrow exceptions.
One of those exceptions that might have applied was for requirements under "a state law regarding motor vehicle license plates or other displays that the Secretary [of Transportation] determines are appropriate."
FMCSA asked for public comments on the challenges, and received responses only from industry representatives, all of which argued for preemption. In addition, Cook County wrote to FMCSA admitting that its requirement could not be enforced.
In its decision, the agency ruled that all three credentials were prohibited under Section 14506, since they did not meet any of the exceptions provided for by the law.
The decision may be found here.