Conservative groups perpetuating Donald Trump’s false charges that the 2020 election was rigged have sparked a lawsuit against one in Colorado, and a congressional panel investigation of another in New Mexico, over aggressive tactics allegedly used to seek out possible voter fraud.

The scrutiny and criticism facing these conservative groups underscore how Trump loyalists in several US states are working to sustain falsehoods about Trump’s loss, while launching new drives that voting rights advocates say smack of voter intimidation, often targeting communities of color.

A lawsuit was filed by the NAACP and two other groups in March charging that Colorado-based US Election Integrity Plan (USEIP), which has echoed Trump’s baseless claims about 2020 election fraud, has gone door to door in some counties aggressively questioning residents about their voting status and sometimes bearing arms.

Moreover, the House Committee on Oversight and Reform has been investigating EchoMail, a firm that helped push false claims of election fraud in Arizona and has reportedly been paid $50,000 by a New Mexico county to oversee a local “audit force” doing intrusive door-to-door voter canvassing.

Other states including Michigan and Utah boast conservative groups that, under the guise of protecting voting integrity by ferreting out fraud, have been criticized for the methods they employed in seeking out potential voter fraud.

“As Americans, we expect and demand an open and participatory democracy that welcomes all voters equally,” said Danielle Lang, senior director of voting rights at the nonpartisan Campaign Legal Center. “Those engaging in these pressure tactics should know that voter intimidation is a crime with serious consequences.”

The lawsuit against USEIP filed by the NAACP in Colorado, the League of Women Voters in Colorado and Mi Familia Vota charges that USEIP has engaged in “door-to-door voter intimidation”, including taking pictures of some houses, in neighborhoods with a large number of minority residents.

The lawsuit alleges, without providing specific cases, that USEIP representatives have at times worn badges or carried firearms when visiting voters’ residences, although they are not government officials.

“We’re very concerned about reports that Colorado voters have received visits at their homes from people, sometimes openly armed, posing as government officials who imply, without evidence, that fraudulent voting activity occurred at their address,” Beth Hendrix, the League of Women voters executive director in Colorado told the Guardian.

A Colorado judge last week rejected a motion by USEIP to dismiss the lawsuit. A separate motion by the plaintiffs’ two counsels, the nonprofit legal group Free Speech for People and the law firm Lathrop GPM, to obtain a preliminary injunction to halt USEIP’s efforts is pending.

The lawsuit partly rests on a measure that passed after the Civil War, called the KKK Act, aimed at stopping white terrorists from using violence to interfere with Black voters.

USEIP, which started after Joe Biden defeated Trump, is run by Shawn Smith, a retired air force colonel who also leads Cause of America, a nationwide group that boasts that its role is to “enable, facilitate and support citizen grassroots action to restore trust in local elections”.

Mike Lindell, the multimillionaire Trump loyalist who is CEO of MyPillow and has been the chief financier of Cause of America, told the Guardian that the group serves as an “information hub” with a presence in all 50 states and on his website FrankSpeech.com.

Lindell estimated he has spent between $100,000 and $200,000 monthly for salaries for the group’s employees – except for Smith, who is unpaid – and other expenses.

Smith was reportedly tapped by Lindell to run Cause of America last fall, after Smith attended a Lindell-organized “cyber symposium” last summer in South Dakota which promoted conspiratorial and baseless claims of voting fraud in 2020.

An organizing manual for USEIP thanks Lindell, but he told the Guardian that he had no ties with it.

Smith can be seen in a 39-second video clip in a large crowd of Trump loyalists who were at the Capitol during the 6 January assault and another photo that was released by Colorado Newsline and relied on ProPublica research.

Smith did not reply to emails sent to Cause of America seeking comment.

Other outfits with track records for claiming the 2020 election was rigged have popped up in New Mexico, where ostensibly in the name of ferreting out voting fraud, they have sparked concerns about intimidating voters in areas with large minority populations.

Top Democrats on the House Committee on Oversight and Reform in March announced an investigation into allegations from state officials that EchoMail was retained by tiny Otero county to examine potential voting fraud in part by overseeing a door-to-door voter canvass.

The founder of EchoMail, VA Shiva Ayyadurai, has been a frequent promoter of unfounded conspiracies about the 2020 election results as well as a Senate primary in Massachusetts that he lost, and the firm was also a subcontractor for a widely debunked Arizona audit of its largest county.

EchoMail’s contract, according to records obtained and published by the watchdog group American Oversight and first reported by NBC News, called for it to supervise a door-to-door voter canvass by a groupcalled the New Mexico Audit Force, to check the accuracy of voter rolls. The company’s contract also said it would inspect ballot images in the county, and assess voter signatures for accuracy.

The House Oversight Committee chair, Carolyn Maloney, and the chair of its subcommittee on civil rights and civil liberties, Jamie Raskin, wrote Ayyadurai in March that it is “investigating whether your company’s audit and canvass in New Mexico interferes with Americans’ right to vote by spreading disinformation about elections and intimidating voters”.

The House letter pointed out that 40% of the county’s residents are non-white Hispanic, and raised the concern that the company’s canvas could “have a particular impact on minority communities in Otero county”.

Otero county, which has a population of 67,000 people, was won by Trump by more than 25% of the vote in 2020.

In response, Ayyadurai denied EchoMail was playing any such role in Otero county and did not provide requested documents, prompting another letter to Ayyadurai with evidence and statements from a New Mexico couple involved in the “audit force”.

A committee spokesperson told the Guardian that “Dr Ayyadurai has denied EchoMail’s participation in the sham audit and canvass, directly contradicting statements made by leaders of the New Mexico Audit Force and raising serious doubts about his credibility”.

The panel is now weighing its next moves “to get to the bottom of this so-called audit and prevent other attacks on our elections”, the spokesperson added.

The oversight committee also wrote in March to justice department assistant attorney general Kristen Clarke of the civil rights division to share its concerns about possible negative impacts of EchoMail’s Otero county efforts.

On a related voting front, congresswoman Maloney told the Guardian in a statement that another investigation she launched last month with congresswoman Zoe Lofren, the chair of the House administration committee, is looking into “election disinformation in Arizona, Florida, Ohio and Texas. This is a fight for our democracy, and I am committed to finding solutions.”

Lang of the Campaign Legal Center stressed that groups trying to find fraud while harassing voters or spreading disinformation won’t succeed and will be challenged. “The right to vote is the bedrock of our society and voters won’t be bullied out of exercising their rights,” Lang said.