An upstate New York resident sued US Immigration and Customs Enforcement (ICE) for sending federal officers to his house with a warning over an email he sent to the agency’s one-time head.

David Streever, who is a US citizen, was on a trip to Finland when two officers showed up to his Rochester home in June and presented his wife with a warning notice informing him that the email he sent months earlier was considered a threat, his attorneys said. Streever sent the email in January to Todd Lyons, then the acting director of ICE, after an immigration officer fatally shot Minneapolis resident Renee Good in a confrontation caught on video during an anti-ICE demonstration.

In the email, Streever called Lyons “a monstrous human being” who “will never know peace”. He said the agency violated his rights under the US constitution’s first amendment – which include free speech – in a lawsuit filed on Monday in Washington DC.

Streever is one of at least two residents of upstate New York who was served with a federal warning in June in the wake of criticizing ICE online. The Philadelphia-based Foundation for Individual Rights and Expression is representing Streever – and said it filed the lawsuit because Streever’s right to free expression was violated.

“This is very clearly within the protection of the first amendment,” said Adam Steinbaugh, an attorney with the foundation. “It was in the context of political speech.”

Representatives for ICE previously declined to comment on the warning to Streever, citing an ongoing investigation. And the agency did not immediately comment Monday.

The suit also names Markwayne Mullin, the secretary of homeland security, which oversees ICE. Mullin’s office released a statement that said: “Any allegation DHS and its components are attempting to ‘squash’ free speech is categorically FALSE.”

The statement added: “Anyone who assaults or threatens our law enforcement officers will face the consequences.”

Streever’s three-paragraph email carried the subject line “What’s next” and referenced a leader in Nazi Germany.

“You are a monstrous human being and will go down in history as America’s Reinhard Heydrich, the butcher,” the email said. “The way you are protecting the obvious execution in Minnesota, even as we see the videos, will lead to your downfall. Even Trump will turn on you before the end, and you will be a sad, despised man who eats himself alive with shame at your own pathetic weakness.

“You will never know peace. You will seek to lose yourself, to escape the burden of knowing the truth about yourself. But wherever you go, you will find yourself. You will torment yourself until your last day on Earth.”

Federal agents also attempted to confront Streever at a hotel in New York City when he returned from Finland – but they were turned away by hotel staff, Steinbaugh said.

Federal officials went to Streever’s house the same week that officials visited Paigelynne Gonyea, a poll worker, at a voting location during New York’s primaries to confront her about a social media post.

Gonyea believes the warning stemmed from writing “I think today is a great day for Jonathan to be indicted,” in a post with a picture of Jonathan Ross, the ICE officer who shot and killed Good. She posted it in January, after Ross had already been identified by the news media.

A homeland security department spokeperson, Lauren Bis, shared an image of a different social media post from Gonyea in which she said Gonyea shared Ross’ address. Part of that post was redacted.

Bis said in a statement in June that Gonyea “committed a federal crime by posting the address of an ICE law enforcement officer online” – and “if you doxx [sic] our officers, we will investigate you, and you will be brought to justice”.

A representative for the New York attorney general’s office has said the office is aware of the two residents’ contact with federal agents. The representative has said the office has been reviewing the interaction between Gonyea and federal agents that took place at the polls.