According to The Hollywood Reporter, Blunt said news of women being denied entry was "very disappointing".
She said: "Everyone should wear flats, to be honest. We shouldn't wear high heels anyway, that's my point of view.
"You kind of think that there's these new waves of equality and waves of people realising that women are just as fascinating and interesting to watch, and bankable."
Denis Villeneuve, the director of Sicario in which Blunt stars, was also planning his own protest, jokingly telling a press conference that he, Benicio Del Toro and Josh Brolin would walk the steps in high heels.
Others waded in on Twitter.
Festival organisers have since moved to deny claims high heels are obligatory, with director Thierry Fremaux tweeting that rumours women must wear heels on the steps are "unfounded".
A spokesperson told the BBC: "Rules have not changed throughout the years (tuxedo, formal dress for gala screenings) and there is no specific mention about the height of the women's heels as well as for men's."
Screen wrote that a group of women in their 50s, some of which were suffering medical conditions, were denied access to the film Carol because they were wearing rhinestone flats.
A source told the outlet: "I've heard this happening several times now, even to older women who can't wear heels for medical reasons. It's b*******.
"Someone I know was turned away for wearing nice flats, nothing you would wear to the beach. They told her she could go and buy appropriate shoes and come back."
Ironically, the controversy comes as the subject of women in film is discussed avidly at the festival.
Over the past year, numerous high-profile women in film have publicly addressed the gender gap in cinema, urging it to be narrowed and to provide more women with opportunities both on and behind the camera.
- Daily Mail
