Leaders of several hundred education nonprofits, charter school networks, and other education groups have signed onto an open letter expressing “unequivocal disagreement” with the travel ban President Trump instituted last month.

The letter, posted on Medium, is narrowly focused on the executive order Trump signed in late January banning people from seven Muslim-majority countries, as well as refugees, from entering the U.S. Though that order has since been blocked by federal courts, the letter has continued gaining signatures, reaching 438 by this Thursday — indicating that education leaders are increasingly open to weighing in on political matters that they think connect to their mission.

“Groups like ours exist to help lift up the poorest and most marginalized with innovative solutions,” the letter says. “In our opinion, this ban will make our work to foster peace, sustainability, opportunity and inclusiveness much harder.”

Its signers include leaders of the KIPP, YES Prep, DSST, Achievement First, and Uncommon charter school networks; leaders of organizations that provide social services in schools, like Partnership with Children, Good Shepherd Services, and the Center for Supportive Schools; and leaders of mentoring and after-school organizations like Citizen Schools, Groundswell, and OneGoal. Other names include Wendy Kopp, the Teach for America founder, and Lola Hurst, the 11-year old founder of the organization D.C. Bully Busters.

The letter does not touch on new U.S. Education Secretary Betsy DeVos, or address issues like the recent increase in raids targeting undocumented immigrants or the rescinding of federal guidance about protections for transgender students in public schools. But the uncertainty facing undocumented immigrants in particular have prompted leaders of school districts like New York City and Denver to speak out in recent weeks.

Others have faced criticism for staying silent: Politico reported this week that Eva Moskowitz, founder of New York City’s Success Academy network of charter schools, had heard from staff members concerned she wasn’t doing enough to speak up for her students, some of whom are undocumented.

“My position as a public figure and national education leader limits the expression of my personal views,” Moskowitz said in a letter to staff.