Flyers promoting white nationalism were found Sunday on the George Washington University campus in Washington D.C., making it the latest school to fall victim to such an incident.

One poster, addressed “to all white Americans,” encouraged people to report undocumented immigrants to federal officials. “THEY ARE CRIMINALS. AMERICA IS A WHITE NATION,” the sign said, according to the Washington Post.

The flyers advertised Vanguard America, a group that, in its online manifesto, calls for “a nation exclusively for the White American peoples.” The group did not immediately respond to a request for comment Tuesday.

The incident at George Washington mirrored similar occurrences across the country, as several colleges have also found posters advocating for white supremacy or white nationalism on their campuses in recent months — and many of those posters have also advertised Vanguard America.

The Anti-Defamation League last week released a report warning that hate groups are engaged in an “unprecedented outreach effort” on college campuses. The ADL counted 104 incidents of white supremacist flyers being posted on campuses since the beginning of the school year in September 2016, noting a surge in 2017, when most of those incidents (63) have taken place. The group did not provide data comparing this school year to previous years.

“We are aware that some fliers were posted without authorization on campus. We are in the process of removing them,” George Washington spokesperson Candace Smith said in a statement. “GW Police are investigating to determine the identity of those who have defaced our property. The language used in the fliers is offensive and is counter to our values as an open and inclusive community.”

Smith said the university has previously received reports of similar incidents “mostly post-election,” including the use of racial epithets. But she said the campus had not previously been targeted with fliers, as it was this week.

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Write to Katie Reilly at Katie.Reilly@time.com.