Mark Zuckerberg attacks Donald Trump in F8 keynote

Mark Zuckerberg used the visibility of Facebook’s F8 developer conference to take a thinly veiled swing at Donald Trump’s stance on immigration.

The Facebook founder criticized “fearful voices for building walls” in his opening remarks Tuesday at San Francisco’s Fort Mason center — an obvious reference to the Republican front-runner’s calls to erect a wall along the U.S. border with Mexico to halt illegal immigration.

“It takes courage to choose hope over fear,” Zuckerberg said in remarks that were livestreamed.

Zuckerberg has been outspoken on the issue of immigration — and used the global platform of Facebook to counter some of Trump’s anti-immigrant rhetoric, such as the billionaire real estate mogul’s call for a “total ban” on Muslims entering the U.S.

“As a Jew, my parents taught me that we must stand up against attacks on all communities. Even if an attack isn’t against you today, in time attacks on freedom for anyone will hurt everyone,” he wrote. “If you’re a Muslim in this community, as the leader of Facebook I want you to know that you are always welcome here and that we will fight to protect your rights and create a peaceful and safe environment for you.”

At F8, Zuckerberg argued that immigration is essential to the country’s economic vitality.

“Instead of building walls, we can help build bridges,” Zuckerberg said. “Instead of dividing people, we can connect people.”

The Facebook founder’s political advocacy group, Fwd.us, has been aggressively campaigning against Trump’s call for mass deportation, producing online videos that explore the economic and human toll of removing an estimated 11 million people living in the U.S. without proper documentation.

This article originally appeared on Recode.net.