The "Harry Potter" author's tweets were in response to an opinion piece titled, "Creating a more equal post-COVID-19 world for people who menstruate." Rowling made fun of the article for not referring to those who get their periods simply as "women."
"'People who menstruate.' I’m sure there used to be a word for those people. Someone help me out. Wumben? Wimpund? Woomud?" the 54-year-old wrote.
Twitter users immediately fired back, calling the comments anti-trans because transgender, non-binary and gender-nonconforming people can also menstruate. Rowling responded that it's "nonsense" to say that people who think "sex is real" are "hateful" and that she's "(speaking) the truth."
"If sex isn’t real, there’s no same-sex attraction," she tweeted. "If sex isn’t real, the lived reality of women globally is erased. I know and love trans people, but erasing the concept of sex removes the ability of many to meaningfully discuss their lives."
Rowling added that she "(respects) every trans person’s right to live any way that feels authentic and comfortable to them."
She went on to justify her opinions, saying that she's well-educated on trans issues.
"I’ve spent much of the last three years reading books, blogs and scientific papers by trans people, medics and gender specialists," she tweeted. "I know exactly what the distinction is. Never assume that because someone thinks differently, they have no knowledge."
The responses to her assertions on social media were swift and emphatic.
"The vast consensus of medical and other scientific experts validate trans people and urge affirmation of us," one person tweeted. "Your own country’s medical organizations have said as much. You don’t love trans people, and certainly don’t care about us."
"You’re a smart person," replied another. "How do you not yet understand the difference between sex and gender? The only way I can possibly explain your ignorance at this point is willfulness. It’s incredibly disappointing."
LGBTQ advocacy group GLAAD called Rowling's comments "inaccurate and cruel" in a series of tweets and a statement sent to TODAY.
"J.K. Rowling continues to align herself with an ideology which willfully distorts facts about gender identity and people who are trans," the organization said. "In 2020, there is no excuse for targeting trans people ... We stand with trans youth, especially those 'Harry Potter' fans hurt by her inaccurate and cruel tweets."
GLAAD also recommended that fans angered by her comments take the opportunity to support organizations that help black trans people.
Referencing another popular, young adult, fantasy series, GLAAD concluded, "By the way, looking for some summer reading? 'Percy Jackson' author Rick Riordan isn't transphobic."
Celebrities, including Broadway actor Anthony Rapp, also joined the conversation.
Rapp's pointed tweet read: "She has such a powerful voice. Why is she using that voice to die on a hill of transphobia? It is damaging and sad and makes zero sense. Is it really her belief that trans women somehow threaten her own selfhood?"
"Goodnight and shut up," actress Sarah Paulson added.
This isn't the first time Rowling has been called out for anti-trans comments. In December, she was widely criticized for supporting a researcher who lost her job after saying she did not agree that "trans women are women."
At the time, Rowling wrote: "Dress however you please. Call yourself whatever you like. Sleep with any consenting adult who'll have you," Rowling wrote Thursday in her first tweet since September. "Live your best life in peace and security. But force women out of their jobs for stating that sex is real?"
Spokespeople for Rowling declined TODAY's request for comment.