WASHINGTON – When Homeland Security Secretary Kirstjen Nielsen went on national television Monday and dismissed criticism over the child separation policy — falsely pinning it on a "law passed by the U.S. Congress" — a special level of outrage was felt by graduates of Berkeley Preparatory School in Tampa.

Nielsen, who a day earlier denied a policy even existed, graduated from the school in 1990.

Her role in the controversy has mobilized fellow Berkeley Prep graduates, who have written an open letter to the school's headmaster, Joseph Seivold, calling on him to join in condemnation.

More than 500 of people have signed the letter and organizers have raised more than $6,000 for a Texas nonprofit that provides services to immigrant children and families.

"During our years at Berkeley, we were often reminded of the school's creed: Berkeley puts people in the world who make a positive difference," the letter reads. "The impact of this mission statement is apparent in our alumni, with many of us choosing to fight injustice in our professions — as lawyers, labor organizers, nonprofit professionals, health advocates, and journalists — but for all of us, not a day goes by that we do not consider the impact of our actions, or inactions, upon the world around us.

"For this reason, we would be remiss to stay silent now. Today, we respectfully request that you condemn the policies causing the separation of children from their families at the US-Mexico border, implemented and enforced by Secretary of Homeland Security Kirstjen Nielsen — known to us as Kirstjen Nielsen, Class of 1990."

Read more: A Tampa Bay 'superstar' caught in the crosshairs of Trump's border policy

Nielsen, 46, went to Georgetown and became an aide to Sen. Connie Mack, R-Fla., then joined the George W. Bush White House. She was confirmed as Homeland Security secretary in December 2017, with the support of Florida Sens. Bill Nelson and Marco Rubio.

As Trump pursues tough border measures, Nielsen has felt herself in the crosshairs, drawing heat from the president himself, worried he has not fulfilled campaign promises on immigration. At one point, she nearly resigned.

But the child separation issue has brought things to a new level. Democrats have called for Nielsen to resign. Last night in Washington, protesters shouted "shame" while Nielsen dined at MXDC Cocina Mexicana near the White House.

"We recognize that it would be easy to dismiss our request as absurd or out of your purview — it would be, in many ways, disadvantageous to Berkeley to chime in," the Berkeley letter reads. "But morality transcends respectability, and today children are removed from the protection of their parents to instead be kept in cages, some even driven to suicide by a graduate of our institution. This issue runs deeper than partisan politics, and treating it as a purely political dispute would secure a spot for our school on the wrong side of history. So we invite Berkeley's administration, faculty, staff, alumni, and students to stand with us and be a voice for integrity and compassion. Berkeley taught us all to lead by example, and we implore you to join us in doing so."

In a statement, the school said:

"Berkeley Preparatory School is a diverse community comprised of many thousands of students, families, employees, alumni and alumni parents. The school is mission-driven to provide the best possible environment for the intellectual, emotional, spiritual and physical development of each student, and to instill in them a strong sense of morality, ethics, and social responsibility. As a school, Berkeley's charge is not and cannot be to take a position on non-education-related governmental policy or action; it is to foster the confidence and build the critical thinking skills of our students so that they may do so."