Those people said that the application had been under review for roughly two years, and had at one point included a demand — which was not met — for enhanced access to the group’s security-protected website, which would have revealed member names. Tax experts said that an organization’s membership list is information that would not typically be required. The I.R.S. already had access to the site’s basic levels, a request it considers routine for applications for 501(c)(3) nonprofit status.

Friends of Abe — the name refers to Abraham Lincoln — has strongly discouraged the naming of its members. That policy even prohibits the use of cameras at group events, to avoid the unwilling identification of all but a few associates — the actors Gary Sinise, Jon Voight and Kelsey Grammer, or the writer-producer Lionel Chetwynd, for instance — who have spoken openly about their conservative political views.

The I.R.S. request comes in the face of a continuing congressional investigation into the agency’s reviews of political nonprofits, most of them conservative-leaning, which provoked outrage on the right and forced the departure last year of several high-ranking I.R.S. officials. But unlike most of those groups, which had sought I.R.S. approval for a mix of election campaigning and nonpartisan issue advocacy, Friends of Abe is seeking a far more restrictive tax status, known as 501(c)(3), that would let donors claim a tax deduction, but strictly prohibits any form of partisan activity.

The group is not currently designated tax-exempt, but it behaves as a nonprofit and has almost no formal structure, people briefed on the matter said. The I.R.S. review will determine whether Friends of Abe receives tax-exempt status that would provide legal footing similar to that of the People for the American Way Foundation, a progressive group fostered by the television producer Norman Lear and others. If not, Friends of Abe could resort to the courts, or it might simply operate as a nonprofit, but it would be unable to receive tax-deductible contributions.

Jeremy Boreing, executive director of Friends of Abe, declined on Wednesday to discuss details of the tax review, but said the group would continue regardless of outcome.