Many beneficiaries of the tax break are campaign contributors to the lawmaker, Representative Charles B. Rangel, Democrat of New York, according to data collected by CQ MoneyLine, which tracks political contributions.

At least one of them, Richard G. Vento, is currently under audit, according to court filings. Mr. Vento gave $4,400 last year to the Baucus-Rangel Leadership Fund, which supports Mr. Rangel and Senator Max Baucus, the Montana Democrat who heads the Senate Finance Committee.

Beneficiaries of the tax break including Michael W. Masters and Richard H. Driehaus, money managers, accounted for more than half the $51,900 that individuals in the Virgin Islands gave last year to Rangel for Congress, the chairman’s campaign organization. Mr. Rangel raised almost three times as much from such donors last year as in any other year in the MoneyLine database.

Mr. Rangel says his measure is simply an effort to address a discrepancy between the Internal Revenue Service’s treatment of Americans living in the Virgin Islands and its treatment of their mainland counterparts. Except in cases of fraud, the agency has three years to cite errors in a mainland resident’s tax payments. But since 2006, under I.R.S. rulings stemming from the agency’s efforts to crack down on abuse of the tax break, it has faced no such time limit in auditing Virgin Islands residents.

The Rangel provision would restore the statute of limitations in the islands.

“This is a fundamental matter of fairness,” the congressman said in a statement. “U.S. citizens living in the Virgin Islands should be afforded the same protections as citizens living here.”

As to whether donations from such taxpayers had influenced his decision to offer the proposal, he said, “I am overwhelmed with appreciation for the support I have received from across the nation, and I am certain that I have had supporters from the U.S.V.I. well before the question of legislation ever came about.”

The provision is in a broader tax relief bill intended to prevent some 21 million American households from falling subject to the alternative minimum tax this year. That broader bill was approved by Mr. Rangel’s committee last week.

The Virgin Islands tax break — an effective federal tax rate of only 3.5 percent on income earned in the islands — is tied to a program to encourage economic development there. It has existed since the 1960s, but it gained momentum over the last decade as the Virgin Islands government opened the program to services companies in an effort to attract educated, affluent workers.

Financial services companies and their executives began flocking to the islands, taking steps like contributing to local charities as ways of establishing residency, which was required to capitalize on the program’s tax benefits.

The I.R.S. became suspicious that many were spending more time running their businesses on the mainland than in the islands, and in 2003 it undertook enforcement efforts that, lawyers in the islands say, have ensnared some 100 taxpayers, not all wealthy.

Mr. Rangel’s proposal would end any such audits involving years before 2004. That upsets Senator Charles E. Grassley, an Iowa Republican responsible for legislation that year that tightened rules governing taxes on Americans in the Virgin Islands.

“Congress rarely takes action that affects ongoing I.R.S. audits,” Mr. Grassley said in a statement, “so it’s striking that House leaders are proposing changes in the statute of limitations for U.S. taxpayers who are newly claiming residency in the Virgin Islands.”

Marjorie Rawls Roberts, a lawyer who represents Mr. Vento and other Virgin Islands residents, said some of her clients might benefit from the provision, but not all of them.

“The limits would end some audits at least for some years,” Ms. Roberts said. “At the same time, the I.R.S. has sought and received timely extensions from some taxpayers, including Mr. Vento, and in cases where extensions have been granted, the new limits would not apply.”

Ms. Roberts, who is herself a donor to Mr. Rangel, and other lawyers said the agency had closed only a handful of the audits undertaken. At least one beneficiary of the tax break has pleaded guilty to tax fraud, and four others were indicted on tax and wire-fraud charges in March.

Mr. Vento is fighting the I.R.S. in court over its claim that he was not a bona fide resident of the Virgin Islands in 2001, when he made some $180 million from the sale of a company he had founded, and that he therefore owes back taxes. In the meantime, the agency continues to look at subsequent years.

Some lawyers speculate that the I.R.S. eliminated its time limit last year simply because inquiries involving the tax break were multiplying faster than it could handle them.

“I think they are conducting audits that are spinning out of control, and so some genius decided to just get rid of the statute of limitations,” said David Marshall Nissman, a former United States attorney for the Virgin Islands who says he has five or six clients currently under audit.

Mr. Nissman said many newer participants in the economic development program withdrew from it after it came under intense scrutiny from Congress and news organizations in 2004. “I think for the most part the abusers are gone,” he said. “But I’m sure there are still a few."