Standing for Women, headed by Kellie-Jay Keen – also known as Posie Parker – staged a protest in Glasgow on Sunday against the Scottish Government's gender recognition reform proposals, which were passed by a majority of MSPs in December, but blocked by the UK Government.
Speaking in George Square, Ms Keen also attacked the Scottish Government over the case of Isla Bryson, who raped two women when she was a man called Adam Graham before transitioning.
Bryson was imprisoned in segregation at Cornton Vale women's jail near Stirling upon her conviction, before being moved to the male estate after a public outcry.
Speaking to the assembled crowd, Ms Keen said: "Nicola Sturgeon said it would never happen and all of us knew it was already happening and then along came Adam 'double-rapist' Graham, who said 'it absolutely happens all the time and look at me'.
"I just want to thank the SNP for waking up Scotland, and to all the Scottish women and some of you men who have been campaigning about this for the last five years."
Ms Keen said those attending the rally were "here to be counted and we will be seen".
Her group has called for the repeal of the Gender Recognition Act, the existing legislation that allows transgender people to obtain a gender recognition certificate the Scottish Government's Bill was attempting to reform.
She told those at the protest: "In your own lives, you cannot be heard ... you feel like you cannot speak … the watershed is finally here.”