The argument is that the Japanese bank employs mostly males.
The city's plumbing code requires restrooms for men and women be equal unless they get approval otherwise.
From the city's plumbing code [.PDF]:
403.3 Number of occupants of each sex. The required water closets, lavatories, and
showers or bathtubs shall be distributed equally between the sexes based on the
percentage of each sex anticipated in the occupant load. The occupant load shall be
composed of 50 percent of each sex, unless statistical data approved by the commissioner indicate a different distribution of the sexes.
Nomura's population on these lower level floors, which the Post believes are most likely the trading floors, is 75 percent male and 25 percent female.