The City of Denver, Latino civil rights organizations and government watch groups asked a federal judge on Thursday to block the Trump administration from allowing armed federal immigration agents to serve warrants at polling sites. The lawsuit, filed in federal court in Washington, D.C., asserts that Markwayne Mullin, the homeland security secretary, and David Venturella, the acting head of Immigration and Customs Enforcement, are allowing federal agents to enforce civil immigration laws at polling locations as a matter of policy. The plaintiffs argue that the practice violates federal laws protecting free and fair elections.

“The presence of federal force at the polls interferes with the smooth administration of elections at the local level,” the lawsuit states. “It disrupts voting and makes it more difficult for state and local election officials and law enforcement to do their jobs by making polling places spaces of confrontation.” The Department of Homeland Security and ICE did not immediately respond to requests for comment.

Speaking to reporters last week in New York, Mr. Mullin said that Democrats were fear-mongering and that ICE was not patrolling polling places. “The only reason why we would be at polling places is if there is a threat to that polling place,” he said, “or we’re serving a warrant.” The groups that brought the suit argue such actions violate federal law, which bans military personnel or other “armed” agents from being “at any place where a general or special election is held, unless such force be necessary to repel armed enemies of the United States.”

Their case is the first lawsuit against the administration over such actions. Civil rights and government watch groups say they have chronicled several encounters at polling sites nationwide since the spring that they said failed to meet that bar. In May, they allege, armed agents “swarmed” the parking lot of an active polling site in San Antonio to detain a person in plain view of voters until the county sheriff ordered them leave. In June, ICE agents entered a polling site in Syracuse, N.Y., to interrogate an election volunteer over a social media post that she made five months earlier regarding the fatal ICE shooting of a woman in Minneapolis, according to the lawsuit.