Section 1050.9(h)1
of the MTA Rules of Conduct states:
[…] no person may bring any animal on or into any conveyance or facility unless enclosed in a container and carried in a manner which would not annoy other passengers.
I would venture as far as to state that this good boy or girl isn't annoying anybody, and is clearly in a "container", thus, a perfectly legal subway dog.
via reddit
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