A bus carrying mostly Hasidic Jews - where men sit at the front and women sit at the back - has provoked fury from the New York City Mayor.
Michael Bloomberg said gender segregation on public buses is 'obviously not permitted' and called the bus in Brooklyn, New York, an 'outrage'.
From the outside the B110 might look like any other bus - but on the inside revelations about its seating arrangements are causing huge controversy.
The unusual practice has only come to light after a woman told a student newspaper other riders said she had to leave the front and sit in the back.
The B110 has been operated by the Private Transportation Corporation for 38 years under a city franchise, reported the New York Times.
The bus's outer colours are red, white and blue, it costs $2.50 to ride and it is out of action on Friday night and most of Saturday.
'It's such a normal thing for us that women and men are separate,' rider Gitty Green told the New York Times. 'Most of the ladies go to the back.'
The bus should be 'available for public use' because it was awarded the route in a public bid, a city transport spokesman told the New York Times.
The department has asked bus firm president Jacob Marmurstein to provide it with any complaints made about the separation. He has not yet commented.
There are guidelines in the bus saying if it is crowded then women should pay the driver in the front before boarding in the back.
'I don't like it,' regular rider Asaf Amitay told the New York Times. 'The women is in the back. The men are in the front.'
There are 165,000 Hasidic Jews in New York, with the majority of them living in Brooklyn, and they follow strict religious rules.
They are not allowed to sit with people of the opposite sex who are not their spouse. Their roots are traced back to 18th-century Eastern Europe.