In the wake of Donald Trump’s victory as the U.S. president-elect, some social media users are staging a “blackout” in protest.

The #TwitterBlackout movement (which has also spread to Instagram, Facebook, and Tumblr) gained momentum Wednesday morning, as thousands of users swapped out their profile photos and header images for plain black boxes.

Katy Perry, Questlove, and Emily Ratajkowski were among the earliest celebrity supporters of the movement, changing their avatars and header images in solidarity. Perry — who’s the most-followed user on Twitter — also posted several anti-Trump tweets following the election results. “Do not sit still. Do not weep. MOVE. We are not a nation that will not let HATE lead us,” she wrote, later adding, “Fight for what is RIGHT.”

The #TwitterBlackout movement is a small but significant way people are trying to “create unity” in a seemingly divided country. Many also sent supportive messages to women, people of color, Muslims, LGBTQ Americans, and others who were targeted by Trump during his campaign or who might be feeling particularly vulnerable now that he’s won the White House.

As the movement continues to grow, it’s also being used as an entry point for those hoping to take their protesting offline.