"I want to apologize to the organizers of the Women's Convention for not being able to attend your conference next Friday in Detroit," the Vermont lawmaker said in a statement. "Given the emergency situation in Puerto Rico, I will be traveling there to visit with San Juan Mayor Carmen Yulín Cruz and other officials to determine the best way forward to deal with the devastation the island is experiencing."
In Puerto Rico, about 1 million Americans remain without running water and 3 million without power, CNN reported Wednesday.
Sanders' announcement comes a week after the Women's Convention received backlash
for picking him as a speaker for opening night of the convention.
The three-day event, which will take place in Detroit beginning next Friday, "aims to have participants leave inspired and motivated, with new connections, skills and strategies for working towards collective liberation for women of all races, ethnicities, ages, abilities, sexual identities, gender expressions, immigration statuses, religious faiths, and economic statuses," according to its press release.
The Women's Convention organizers -- who also led the Women's March in January -- stood by their decision to have Sanders attend, despite the mixed reactions.
"Sorry. I'm not attending a women's convention where the opening night speaker isn't a woman," one Twitter user wrote, sharing a photo collage of Sens. Elizabeth Warren, Kamala Harris and Amy Klobuchar. "Perhaps consider these choices next time."
In the initial announcement, Tamika Mallory, Women's March co-president, described Sanders as the perfect fit for the convention, describing him in a statement as a "fierce champion of women's rights" and someone who has bolstered "female voices throughout his career of public service."
Mallory pointed to the handful of other speakers who will address attendees, including California Democratic Rep. Maxine Waters, whose viral "Reclaiming Our Time" phrase
inspired the theme of the convention.
In a statement provided to CNN Thursday, convention organizers expressed their understanding of Sanders' trip.
"It is unfortunate that Senator Sanders will no longer be able to join us at the Women's Convention next week," the organizers said in an email statement to CNN. "But the humanitarian crisis in Puerto Rico - which is being exacerbated by the inaction of our federal government - is a critical matter. We understand his leadership is needed in Puerto Rico and, as always, we deeply appreciate his commitment to communities in need. We look forward to continuing to work with him on issues that impact women and all Americans."
Sanders concluded his statement by applauding "their historic work in putting together the march in January and all that you have done since," he said. "My best wishes for a very successful conference."
Other speakers at the convention include actress and activist Piper Perabo, political commentator, community organizer and CNN contributor Sally Kohn, The Young Turks reporter Nomiki Konst, co-executive director of the Indivisible Project Leah Greenberg, Michigan Democratic gubernatorial candidate Gretchen Whitmer, Michigan state Rep. Stephanie Chang, Georgia gubernatorial candidate Stacey Abrams and others.