In June last year, Luis, a resident of Virginia, was astonished to discover that his name and personal details, including home address, had been posted on the internet by a group known as the Public Interest Legal Foundation (Pilf).

Luis’s data had been released by the group, along with hundreds of other names, as an appendix to Pilf’s two-part report called “Alien Invasion”. The front cover showed a UFO hovering ominously over a billboard on which the famous tourism slogan “Virginia is for lovers” had been photoshopped to read: “Virginia is for aliens”.

In lurid language, Pilf claimed that it had uncovered proof that “large numbers of ineligible aliens are registering to vote and casting ballots”. It warned its readers: “Your vote is at risk. New alien voters are being added to the rolls month after month, and swift changes must be made to ensure that only Americans are choosing American leaders.”

The only problem was that Luis, in common with dozens of other Virginians on the list posted by Pilf, was not in fact an “alien”. He was born in Los Angeles and has always enjoyed US citizenship, with full rights to vote since the age of 18.

He also happens to be a federal employee of the US immigration service. Yet here he was, his name attached to a report in which Pilf claimed to have discovered more than 5,000 non-citizens in Virginia who had cast 7,474 votes – every one a criminal act amounting to a felony.

The insinuation was deeply troubling to Luis. As a federal worker he could face intense scrutiny as a result of any suggestion of illegal activity (for the same reason he asked the Guardian to use only his first name).

Luis was also disturbed on behalf of hundreds of other people who also had their personal details – names, addresses and in some cases even home phone numbers – posted in the appendices of the Pilf reports. “I thought if my name is on the list, and I’m a US citizen, how many others were wrongly accused of being illegal ‘alien’ voters?”

Alien Invasion is one of the more startling examples of a growing rightwing push to pressurize election officials across the country to purge large numbers of people from the registered voter rolls. With the midterm elections rapidly approaching, and with so much riding at both national and state level on voter turnout, the stakes could not be higher.

Voting rights experts warn that hundreds of thousands of eligible voters could face hurdles as they try to get to polling stations in November. African American, Hispanic or other minority communities, as well as young voters, are especially vulnerable to purges as they more frequently experience the kind of bureaucratic hiccups that can lead them to them being mistakenly ruled ineligible.

They are promoting purges that prevent eligible voters from participating in our democracy Chiraag Bains, Demos

A recent study by the Brennan Center for Justice found that since 2013, when the US supreme court drastically reduced federal controls against discriminatory behavior by largely southern states, there has been a dramatic uptick in voter purges. The numbers affected are breathtaking: between 2014 and 2016 alone, 16 million people nationwide were removed from register rolls.

The US Department of Justice, which has the task of protecting the voting rights of Americans, has increasingly switched its focus under Donald Trump from policing purges to encouraging them. The president has personally championed conspiracy theories about “alien” voters, claiming that 3m illegal votes were cast in the 2016 presidential election – conveniently, precisely the number by which his rival Hillary Clinton won the popular vote.

In June, the US supreme court lent its weight to the wave of purges sweeping the country when it ruled in favor of Ohio’s tough stance in which citizens can be thrown off voter lists simply for missing an election and then fail to respond to official correspondence. Should other states follow in Ohio’s footsteps, the Washington Post estimates that millions of legitimate American citizens who should be fully entitled to participate in the democratic process will be in peril of being cast adrift.

Pilf and its president, J Christian Adams, a former senior official in the DoJ, are at the forefront of the wave. Justin Levitt, one of the country’s foremost election experts who was a senior official in the civil rights division of the justice department and is now a professor of election law at Loyola in Los Angeles, said: “Pilf wants to sweep people off the lists in ways that are unreliable, and poor and transient people are more likely to get knocked off the rolls and then find it harder to get back on.”

The front page of Pilf’s ‘Alien Invasion’ booklet. Photograph: Public Interest Legal Foundation

Chiraag Bains of the advocacy group Demos that has monitored the activity of Pilf and its allied groups for several years, said: “Their aim is not to ensure the security of our elections, but to intimidate people from going to the polls. They are promoting purges that prevent eligible voters from participating in our democracy.”

Pilf and Adams are now being sued for defamation and voter intimidation over Alien Invasion. The case, lodged with a federal court in Richmond, Virginia, has been brought in the names of three plaintiffs: Eliud Bonilla, Luciania Freeman and Abby Jo Gearhart. The three were among Pilf’s “alien” names yet, like Luis, turn out to be US citizens born in this country with full voting rights.

Pilf drew its information for Alien Invasion from Virginia’s “declared non-citizen” registry, into which people whose eligibility to vote is uncertain are put for verification. Election supervisors have pointed out that individuals can be put into that category for a variety of reasons including failure to respond to official letters or clerical errors – in other words, inclusion in the pile is not confirmation that you are a non-citizen.

In the case of Luciania Freeman, for instance, a state official appears to have mistakenly assumed she lacked citizenship by misreading a motor vehicle form.

The lawsuit argues that the three citizens were defamed under Virginia law by being negligently depicted as “aliens” engaging in criminal voting. The suit also invokes a rarely used section of the Ku Klux Klan Act that was originally designed as a way of preventing KKK night riders from intimidating African Americans from going to the polls.

“Voter intimidation looks different today – nobody needs to wear white hoods or burn crosses,” said Allison Riggs from the Southern Coalition for Social Justice who is lead counsel on the case. “Instead, you accuse people of crimes when they’ve done nothing wrong and put their names out there for the rabid masses to fixate on: that’s insidious modern-day intimidation.”

Pilf declined to tell the Guardian what steps it had taken, if any, to verify the status of the people whose names it posted. But Adams insisted in an email that voter fraud was widespread in US elections, and thus his Alien Invasion investigation was justified.

He said: “People who deny that voter fraud is occurring and that aliens are voting in sizeable and unacceptable numbers are flat-earthers.”

Leading academics, however, disagree with him. Studies have concluded that “by any measure, voter fraud is extraordinarily rare”.

Last month Adams attempted to persuade a federal district judge to dismiss the Alien Invasion lawsuit, but failed. In court documents, Pilf said all the names attached to the reports had come from public voting records.

J Christian Adams denied that Pilf is in the business of voter purges. “We’ve never done ‘purges’. We encourage states and election officials to use all the tools available to keep lists accurate,” he told the Guardian.

But Pilf, often working in tandem with similar-minded rightwing organisations such as the American Civil Rights Union, Judicial Watch and True the Vote, has targeted hundreds of electoral jurisdictions in recent years. Last September it sent out a letter threatening legal action to 248 election supervisors, accusing them of managing bloated voter lists.

With the clock ticking to the midterm elections, attempts to block people from voting through purges are likely to grow more intense. Adams himself scoffed when the Guardian asked him whether the lawsuit had put him off similar efforts in future.

“Are we dissuaded?” he said. “Hardly. More [Pilf] reports are coming, and so are more efforts to improve voter rolls across the country. No chance that is stopping.”

As for Luis, he too scoffed when the Guardian asked him whether Alien Invasion had put him off trying to vote. “On the contrary, I want to vote now more than ever,” he said. “Usually I don’t vote in midterms, but after what they did to me – this year I definitely will.”