The move by ANA has sparked controversy because many men feel that they will be getting a raw deal. With fewer lavatories to choose from when flying, men may have to stand in line for longer on flights that offer women-only toilets. 

Barry Smith, Skyscanner Co-founder and Development Director said "Women-only lavatories are great for the girls, but the problem is that most planes would not be adding extra toilets, instead they would convert a uni-sex restroom into a ladies-only one. This is bad news for the boys as it's likely to mean longer lines." 

Comments from some of the respondents show this split in opinion "We need women-only toilets because men make so much mess" said one voter. But another countered: "If they introduce women-only lavatories, then they should introduce men-only ones, too. Women take ages." 

The onboard restroom riddle joins the other great toilet debate that has been at the heart of a long running row between men and women ever since the WC was invented, should the toilet seat be left up or down? 

Cheap flights carrier Ryanair caused controversy last year when it joked that it might start charging people to use its toilets.

All passengers, male and female, should be treated equally, said the National Coalition For Men (NCFM). The NCFM has respectfully asks that ANA not employ women-only bathrooms on flights to and from California airports.