For example, the Uranium One chairman, Ian Telfer, used his family charity, the Fernwood Foundation, to make his donations to the partnership. Mr. Telfer would have received a tax benefit when he first put his money into Fernwood, not when Fernwood donated to the partnership.

Image Mr. Giustra and Eric Nonacs, an aide to former President Bill Clinton, helped establish a Canadian charity that feeds donations to the Clinton Foundation. Credit... Mark Mushet

“There would only be one tax benefit no matter how many charities it passes through,” said Mark Blumberg, a tax lawyer in Toronto.

The partnership might have been necessary to provide a tax benefit to early individual donors, but not since 2010. That year, the Clinton Foundation was specially designated by the Canadian government, allowing Canadians to write off donations given directly to it.

“It makes no tax difference,” Mr. Blumberg said, “whether a donor gives the money to a Canadian charity or the Clinton Foundation.”

Because of longstanding concerns about potential conflicts of interest, the Clinton Foundation agreed to strict limits on foreign government donations while Mrs. Clinton served as secretary of state. The existence of the Canadian Clinton Giustra partnership has implications for the foundation’s recent pledge to limit donations from other countries, and disclose all donations quarterly, while Mrs. Clinton is running for president. Ms. Pally said the foundation “will only accept funding from a handful of governments, many of whom the foundation receives multiyear grants from, to continue the work they have long partnered on.”

But the statement did not make clear whether parallel organizations like the Canadian entity would be allowed to accept donations from governments that the foundation itself would not take. The Canadian partnership’s records show that it took donations from outside Canada in 2009 and 2010, the origins of which do not have to be made public. Foundation officials said it was their understanding that the non-Canadian donations to the partnership had not come from governments.

How many more such entities exist, or might be created in the future, is also unclear. A search of charity registrations in Britain, for instance, found a William J. Clinton Foundation UK that has raised about $1.5 million for a climate change initiative. Foundation officials said those donations were made public.