The Homeland Security Advisory Council is made up of 30 members -- both Democrats and Republicans. Some of those who were fired included allies of former President Donald Trump, such as former acting DHS Deputy Secretary Ken Cuccinelli and former acting Immigration and Customs Enforcement Director Thomas Homan.
"I am considering how the HSAC can bring the greatest value to the Department and how the expertise, judgment, and counsel of its Members can be harnessed most effectively to advance the Department's mission. I expect to work closely with the HSAC and to rely on its Members to help guide the Department through a period of change," Mayorkas wrote.
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The HSAC produces reports and advises the secretary on a range of issues from domestic violent extremism to biometrics.
"In the service of an orderly transition to a new model for the HSAC, I have ended the term of current HSAC members effective March 26, 2021," he wrote. "I will reconstitute the HSAC in the next few weeks, once the new model has been developed. Chairman William Bratton and Vice Chair Karen Tandy will remain in their HSAC leadership positions. William Webster will remain the HSAC's Chair Emeritus. I was privileged to work with Judge Webster throughout my prior service in the Department."
Bratton, Tandy and Webster are the only three members still listed on the HSAC website. Bratton, the former NYPD commissioner, serves as commissioner.
Ranking member on the House Homeland Security Committee John Katko, R-N.Y., slammed the action.
"While these members serve at the pleasure of the Secretary, today's action sends the message that this Administration has no intention of upholding a bipartisan, unifying approach to securing our homeland," Katko said. "The HSAC is not intended to be an echo chamber for what the current DHS Secretary wants to hear. Its mission is to provide a knowledgeable, diverse set of perspectives to combat the evolving threats of today and tomorrow."
Trump's former acting DHS secretary, Chad Wolf, who appointed some of the members, tweeted that it was a mistake as well.
"While I respect the right for a DHS Secretary to alter the HSAC to address their needs, dismissing the entire council outright and stopping a lot of important work (that was underway) is not the right approach," Wolf wrote.
ABC News' Mark Osborne contributed to this report.