"The kind of protest that gets rave reviews from the mainstream media for its bravery. Brave? No, not by a long shot," McGowan wrote. "More like an actress acting the part of someone who cares. As so many of them do."
"I find Portman’s type of activism deeply offensive to those of us who actually do the work. I'm not writing this out of bitterness, I am writing out of disgust. I just want her and other actresses to walk the walk."
McGowan then went on to note that the actress has worked with two female directors throughout her career while her production company has only ever hired one - Portman herself.
"As for me, I’ll be over here raising my voice and fighting for change without any compensation. That is activism," the 46-year-old continued. "Until you and your fellow actresses get real, do us all a favor and hang up your embroidered activist cloak, it doesn’t hang right."
In response to the scathing post, Portman released a statement of her own admitting that it is "inaccurate" of media outlets to describe her as "brave".
"Brave is a term I more strongly associate with actions like those of the women who have been testifying against Harvey Weinstein the last few weeks, under incredible pressure," the actress said in reference to the disgraced film mogul's ongoing trial (McGowan was one of more than 80 women to accuse him of sexual misconduct).
Portman then went on to state that although she has only made a few films with women, it has been "incredibly hard" to see them progress from script to screen.
"I have had the experience a few times of helping get female directors hired on projects which they were then forced out of because of the conditions they faced at work," she continued. "After they are made, female-directed films face difficulty getting into festivals, getting distribution and getting accolades because of the gatekeepers at every level."
"So I want to say, I have tried, and I will keep trying," Portman concluded. "While I have not yet been successful, I am hopeful that we are stepping into a new day."