On Capitol Hill and in the courts, Republican lawmakers and activists are mounting a sweeping legal campaign against universities, think tanks and private companies that study the spread of disinformation, accusing them of colluding with the government to suppress conservative speech online.

The effort has encumbered its targets with expansive requests for information and, in some cases, subpoenas — demanding notes, emails and other information related to social media companies and the government dating back to 2015. Complying has consumed time and resources and already affected the groups’ ability to do research and raise money, according to several people involved.

They and others warned that the campaign undermined the fight against disinformation in American society when the problem is, by most accounts, on the rise — and when another presidential election is around the corner. Many of those behind the Republican effort had also joined former President Donald J. Trump in falsely challenging the outcome of the 2020 presidential election.

“I think it’s quite obviously a cynical — and I would say wildly partisan — attempt to chill research,” said Jameel Jaffer, the executive director of Columbia University’s Knight First Amendment Institute, an organization that works to safeguard freedom of speech and the press.

The House Judiciary Committee, which in January came under Republican majority control, has sent scores of letters and subpoenas to the researchers — only some of which have been made public. It has threatened legal action against those who have not responded quickly or fully enough.

A conservative advocacy group led by Stephen Miller, the former adviser to Mr. Trump, filed a class-action lawsuit last month in U.S. District Court in Louisiana that echoes many of the committee’s accusations and focuses on some of the same defendants.

Targets include Stanford, Clemson and New York Universities and the University of Washington; the Atlantic Council, the German Marshall Fund and the National Conference on Citizenship, all nonpartisan, nongovernmental organizations in Washington; the Wikimedia Foundation in San Francisco; and Graphika, a company that researches disinformation online.

In a related line of inquiry, the committee has also issued a subpoena to the World Federation of Advertisers, a trade association, and the Global Alliance for Responsible Media it created. The committee’s Republican leaders have accused the groups of violating antitrust laws by conspiring to cut off advertising revenue for content researchers and tech companies found to be harmful.

The committee’s chairman, Representative Jim Jordan of Ohio, a close ally of Mr. Trump, has accused the organizations of “censorship of disfavored speech” involving issues that have galvanized the Republican Party: the policies around the Covid-19 pandemic and the integrity of the American political system, including the outcome of the 2020 election.

Much of the disinformation surrounding both issues has come from the right. Many Republicans are convinced that researchers who study disinformation have pressed social media platforms to discriminate against conservative voices.

Those complaints have been fueled by Twitter’s decision under its new owner, Elon Musk, to release selected internal communications between government officials and Twitter employees. The communications show government officials urging Twitter to take action against accounts spreading disinformation but stopping short of ordering them to do, as some critics claimed.

Patrick L. Warren, an associate professor at Clemson University, said researchers at the school have provided documents to the committee, and given some staff members a short presentation. “I think most of this has been spurred by our appearance in the Twitter files, which left people with a pretty distorted sense of our mission and work,” he said.

Last year, the Republican attorneys general of Missouri and Louisiana sued the Biden administration in U.S. District Court in Louisiana, arguing that government officials effectively cajoled or coerced Twitter, Facebook and other social media platforms by threatening legislative changes. The judge, Terry A. Doughty, rejected a defense motion to dismiss the lawsuit in March.

The current campaign’s focus is not government officials but rather private individuals working for universities or nongovernmental organizations. They have their own First Amendment guarantees of free speech, including their interactions with the social media companies.

The group behind the class action, America First Legal, named as defendants two researchers at the Stanford Internet Observatory, Alex Stamos and Renée DiResta; a professor at the University of Washington, Kate Starbird; an executive of Graphika, Camille François; and the senior director of the Atlantic Council’s Digital Forensic Research Lab, Graham Brookie.

If the lawsuit proceeds, they could face trial and, potentially, civil damages if the accusations are upheld.

Mr. Miller, the president of America First Legal, did not respond to a request for comment. In a statement last month, he said the lawsuit was “striking at the heart of the censorship-industrial complex.”

The researchers, who have been asked by the House committee to submit emails and other records, are also defendants in the lawsuit brought by the attorneys general of Missouri and Louisiana. The plaintiffs include Jill Hines, a director of Health Freedom Louisiana, an organization that has been accused of disinformation, and Jim Hoft, the founder of the Gateway Pundit, a right-wing news site. The court in the Western District of Louisiana has, under Judge Doughty, become a favored venue for legal challenges against the Biden administration.

The attacks use “the same argument that starts with some false premises,” said Jeff Hancock, the founding director of the Stanford Social Media Lab, which is not a party to any of the legal action. “We see it in the media, in the congressional committees and in lawsuits, and it is the same core argument, with a false premise about the government giving some type of direction to the research we do.”

The House Judiciary Committee has focused much of its questioning on two collaborative projects. One was the Election Integrity Partnership, which Stanford and the University of Washington formed before the 2020 election to identify attempts “to suppress voting, reduce participation, confuse voters or delegitimize election results without evidence.” The other, also organized by Stanford, was called the Virality Project and focused on the spread of disinformation about Covid-19 vaccines.

Both subjects have become political lightning rods, exposing the researchers to partisan attacks online that have become ominously personal at times.

In the case of the Stanford Internet Observatory, the requests for information — including all emails — have even extended to students who volunteered to work as interns for the Election Integrity Partnership.

A central premise of the committee’s investigation — and the other complaints about censorship — is that the researchers or government officials had the power or ability to shut down accounts on social media. They did not, according to former employees at Twitter and Meta, which owns Facebook and Instagram, who said the decision to punish users who violated platform rules belonged solely to the companies.

No evidence has emerged that government officials coerced the companies to take action against accounts, even when the groups flagged problematic content.

“We have not only academic freedom as researchers to conduct this research but freedom of speech to tell Twitter or any other company to look at tweets we might think violate rules,” Mr. Hancock said.

The universities and research organizations have sought to comply with the committee’s requests, though the collection of years of emails has been a time-consuming task complicated by issues of privacy. They face mounting legal costs and questions from directors and donors about the risks raised by studying disinformation. Online attacks have also taken a toll on morale and, in some cases, scared away students.

In May, Mr. Jordan, the committee’s chairman, threatened Stanford with unspecified legal action for not complying with a previously issued subpoena, even though the university’s lawyers have been negotiating with the committee’s lawyers over how to shield students’ privacy. (Several of the students who volunteered are identified in the America First Legal lawsuit.)

The committee declined to discuss details of the investigation, including how many requests or subpoenas it has filed in total. Nor has it disclosed how it expects the inquiry to unfold — whether it would prepare a final report or make criminal referrals and, if so, when. In its statements, though, it appears to have already reached a broad conclusion.

“The Twitter files and information from private litigation show how the federal government worked with social media companies and other entities to silence disfavored speech online,” a spokesman, Russell Dye, said in a statement. “The committee is working hard to get to the bottom of this censorship to protect First Amendment rights for all Americans.”

The partisan controversy is having an effect on not only the researchers but also the social media giants.

Twitter, under Mr. Musk, has made a point of lifting restrictions and restoring accounts that had been suspended, including the Gateway Pundit’s. YouTube recently announced that it would no longer ban videos that advanced “false claims that widespread fraud, errors or glitches occurred in the 2020 and other past U.S. presidential elections.”