It is not the only case of its kind, and what is happening to thousands in Rhode Island could be a harbinger of a much larger pension crisis looming in the United States, experts said.

At issue is a law passed by Congress in 1974 that exempted religious organizations from federal laws that regulated and guaranteed pensions. Decades later, the effects of that lack of oversight are surfacing.

The number of pensioners at risk is unknown , but the potential count could be substantial. The law affects more than just pastors and church organists — religious organizations own vast numbers of businesses, including shopping malls and media companies, and are best known for hospitals, schools and universities.

“It’s estimated to be about a million,” said Dara Smith, senior attorney for the AARP Foundation, which advocates for older Americans, and “that one million figure’s estimated to just be Catholic-affiliated organizations.”

Ms. Smith said the religious exemption waives funding requirements and the mandate for insurance from the Pension Benefit Guaranty Corporation, which pays retirees when there is a shortfall.