RICHMOND, Va. — As one of the keynote speakers here Friday at a state convention billed as the largest Tea Party event ever, Virginia Thomas gave the throng of more than 2,000 activists a full-throated call to arms for conservative principles.

For three decades, Thomas has been a familiar figure among conservative activists in Washington — since before she met her husband of 23 years, Justice Clarence Thomas of the Supreme Court. But this year she has emerged in her most politically prominent role yet: Thomas is the founder and head of a new nonprofit group, Liberty Central, dedicated to opposing what she characterizes as the leftist "tyranny" of President Barack Obama and Democrats in Congress and to "protecting the core founding principles" of the nation.

It is the most partisan role ever for a spouse of a justice on the nation’s highest court, and Thomas is just getting started.

"Liberty Central will be bigger than the Tea Party movement," she told Fox News in April, at a Tea Party rally in Atlanta.

But to some people who study judicial ethics, Thomas’ activism is raising knotty questions, in particular about her acceptance of large, unidentified contributions for Liberty Central. She began the group in late 2009 with two gifts of $500,000 and $50,000 and, because it is a 501(c)(4) nonprofit group, named for the applicable section of the federal tax code, she does not have to publicly disclose any contributors. Such tax-exempt groups are supposed to make sure that less than half of their activities are political.

Thomas, known as Ginni, declined through a spokeswoman to be interviewed without an agreement not to discuss her husband. In written responses to questions, Sarah Field, Liberty Central’s chief operating officer and general counsel, said that Thomas was paid by Liberty Central, with the compensation set by the group’s board, and that the group had "internal reviews and protections to ensure that no donor causes a conflict of interest for either Ginni or her husband."

Nonprofit groups with political agendas like Liberty Central are operating in this election cycle under evolving legal and regulatory standards, most notably the ruling in January by the Supreme Court in the Citizens United case, which eased restrictions on independent campaign spending by corporations and unions. In that case, Thomas, long an advocate of dismantling campaign finance restrictions, was in the 5-4 majority. But they are more important than ever this year as corporations, emboldened by the ruling, look for ways to engage in the election but still hide their tracks.

Unlike many other conservative nonprofit groups that are pouring donations into television advertising to benefit Republican candidates, Liberty Central has not done so and it is not clear whether it will.

This month, Liberty Central began what it called its first ad campaign, but the ads were limited to websites for the conservative talk-show hosts Rush Limbaugh and Mark Levin — suggesting an effort to build membership for Liberty Central, not elect candidates. The ads link to Liberty Central’s website and a video of Thomas soliciting 100,000 signatures against the "Obama tax increase" — referring to the scheduled expiration of the Bush tax cuts Dec. 31.

The bigger question for many is how she is financing these activities. Liberty Central reported the initial $550,000 on its 2009 tax return, although the identities of the two donors are redacted.

A federal law requires justices to recuse themselves in a number of circumstances where real or perceived conflicts of interest could arise, including in cases where their spouses could have a financial interest. But the decision to step aside is up to each justice; there is no appeal from the nation’s highest court.

"It’s shocking that you would have a Supreme Court justice sitting on a case that might implicate in a very fundamental way the interests of someone who might have contributed to his wife’s organization," said Deborah L. Rhode, a law professor and director of the Stanford University Center on the Legal Profession.

"And the fact that we can’t find that out is the first problem," she said, adding, "And how can the public form a judgment about propriety if it doesn’t have the basic underlying facts?"

Steven Lubet, who teaches legal ethics at Northwestern Law School, said Thomas’ solicitation of big contributions raised potential recusal issues for her husband. But he added, "There’s no reason to think that Justice Thomas would be anything other than extremely careful about it."

"I think this is the world we live in, where two-career families are the norm and there are no constraints on the political activities of judicial spouses," Lubet said.

Stephen Gillers, a law professor at New York University, said: "There’s nothing to stop Ginni Thomas from being politically active. She’s a private citizen and she has all of her constitutional rights."

But as for the big donors, Gillers, citing a 1988 Supreme Court decision, said, "She has to tell him because the public is going to assume he knows," and, he said, fair-minded citizens could question Clarence Thomas’ objectivity as a result.

The Supreme Court’s public information office said Virginia Thomas had told court officials of her plans, but it declined to provide any more information.

"Around the time of the launch of Liberty Central, Mrs. Thomas reviewed her involvement with the Supreme Court legal office. Discussions with the legal office that are part of efforts to obtain legal and ethics advice are not made public," Kathy Arberg, the court’s information officer, wrote in an e-mail.

In past interviews, Thomas has suggested she is being singled out unfairly; other spouses of judges are politically active, she has argued, usually mentioning Gov. Edward G. Rendell of Pennsylvania, a Democrat who is married to a judge on the Court of Appeals for the Third Circuit. Rendell has to disclose direct contributions to his campaigns. And parties can appeal to the Supreme Court should his wife not recuse herself when her impartiality is questioned.

Thomas’ political work has drawn criticism before from Democrats. In the weeks before a 5-4 majority of the Supreme Court, including her husband, decided the 2000 election for George W. Bush over Al Gore, Thomas was compiling resumes for potential appointees to a Bush administration from her job at the Heritage Foundation, a conservative, Republican-leaning research group.

Thomas’ supporters said she plays an important role as a bridge between grass-roots Tea Party activists and establishment Republicans in Washington. Ryan Hecker, a lawyer in Houston and a prominent Tea Party activist, said he had heard that Liberty Central was "doing a big get-out-the-vote effort" in some congressional races. Despite the suspicion of many in the Tea Party that Republicans in Washington are trying to co-opt the movement, Hecker said the "charismatic and very genuine" Thomas is not seen that way among activists.

"She’s been there for a long time but she hasn’t been corrupted by it," Hecker said. So she can be "a medium" to get the grass-roots’ views "to the people that matter."

Kitty Bennett contributed reporting.