The genesis for this was when two Canadian sisters were stopped for riding bikes topless. You can read the background to the story here. It has been perfectly legal to be topless in public in Ontario since the mid 1990s, apparently.
One of the sisters, Alysha Brilla is a well known Canadian singer/songwriter.
As is often the case with these things now, Twitter has responded with the hashtag #barewithus
These marches are now getting very familiar, but it shows how far women have to go in the quest of trop-free equality when women will still be stopped for doing something that has been legal for two decades. What do they teach policemen at police training schools?