Women's March organizers angered their supporters Thursday by announcing that Sen. Bernie Sanders will deliver an address on the opening night of its inaugural National Women's Convention, leading to some saying they are boycotting the event and the group.

"This choice sends the wrong message. We've reached out to the @womensmarch organizers to share our disappointment and offer our help," EMILY's List president Stephanie Schriock‏, who heads the political action committee dedicated to increasing the number of women in elected office, wrote on Twitter.

"It's not enough to say we want women to make change — we have to uplift the women leaders doing the work," Schriock‏ added.

The theme for the three-day convention, which is set to take place in Detroit, Mich., beginning Oct. 27, is "Reclaiming Our Time," the phrase Rep. Maxine Waters, D-Calif., coined after she used it repeatedly during a House Financial Services Committee meeting in July.

More than 3,000 women and progressive activists were expected to attend, but some like Amy Lappos are now reconsidering their plans in the wake of the controversial decision to invite Sanders, I-Vt.

"I was so excited for this. Just cancelled my trip to Detroit," Lappos told the Washington Examiner. "How can a man who called Planned Parenthood the 'establishment,' says women's reproductive rights are negotiable, [and] wrote rape fantasies deliver ... [an] opening night speech for women? How can this be?"

She had also "unfollowed" Women's March social media accounts, Lappos continued. She wasn't alone.

"Pretty amazing. How did the WomensMarch not find any woman for this gig? Unfollowing," tweeted Center for American Progress president Neera Tanden.

A representative of Women's March did not immediately respond to the Washington Examiner's request for comment, but the group released a statement on social media after the backlash.

"We invited many elected officials to our convention that align with the purpose and mission of our existence — to harness the political power of diverse women and their communities to create transformative social change," the statement read. "Our program features more than 60 women leading in activism, organizing and advocacy, as well as grassroots leaders running and serving in office across the country. We are excited to come together, to unite across our differences and to fight for the future we all believe in."