As the wave of teacher strikes continues across the United States, immigrant educators in Denver, Colorado, have been uniquely targeted. According to The Guardian, public school officials sent letters in January warning them that they could possibly lose their visas if they decided to join the picket line.

The Guardian obtained a letter to teachers written by Taylor Tanick, a member of the Denver public school system’s human resources team. “In the event that you have teachers who have H or J visas [two types of visas for foreign students and teachers and foreign workers] and that choose to strike, they are allowed to do so,” the letter stated. “But we need to be informed as soon as possible so that we can report that to immigration and the U.S. Department of State. If they have a pending case and they choose to strike, this could impact the decision on the case.”

J-1 cultural visas are given to non-immigrants “approved to participate in work-and study-based exchange visitor programs.” The Guardian estimates “more than 13,000 teachers” were recruited on J-1 visas over the last five years due to local shortages. Additionally, the federal government estimates roughly 18,000 teachers are here on H-1B visas, which allow “companies in the United States to temporarily employ foreign workers in occupations that require the theoretical and practical application of a body of highly specialized knowledge and a bachelor’s degree or higher in the specific specialty, or its equivalent.”

Lily Eskelsen García, the first Latina president of the National Education Association, spoke to The Guardian about the culture of intimidation immigrant educators endure on a regular basis. “Things like that happen all the time,” García says. “And it’s reprehensible. That’s not good faith bargaining—that is an intimidation tactic.”

Union officials responded to the school system’s letter by stating, “under federal law, workers on visas who choose to engage in strikes with their co-workers are protected from deportation.” School officials later apologized for the letter.

Denver Classroom Teachers Association president Henry Roman, an immigrant from Peru, told The Guardian that the effects of the letter still linger. “It resulted in a wave of fear that had a particularly chilling effect on our teachers,” he said. “This is just a scare tactic to intimidate our immigrant educators.”