A new report released Tuesday morning by Americans for Public Trust (APT) claims that six foreign entities have funneled more than $2.65 billion into American politics through U.S. nonprofit organizations. The report was published ahead of a House Ways & Means Committee hearing titled, “Foreign Influence in American Non-profits: Unmasking Threats from Beijing and Beyond.”

According to APT, foreign nationals are barred from donating directly to political campaigns. Still, current law permits funding of 501(c)(3) and 501(c)(4) nonprofit organizations, which can support policy advocacy and political viewpoints.

“Foreign donors can currently fund U.S.-based advocacy groups – most often 501(c)(3)s and 501(c)(4)s – virtually unchecked,” the report alleges. APT adds that the money it identified is “highly concerning” and suggests there is “undoubtedly even more overseas funding sources backing and influencing U.S. advocacy efforts.”

The six foreign entities highlighted in the report are based in Switzerland, Denmark, and the United Kingdom. The largest donor identified is the Switzerland-based Oak Foundation, established by British billionaire retail mogul Alan Parker. According to APT, the Oak Foundation has given approximately $753 million to U.S.-based advocacy groups.

The report states that the Oak Foundation has supported environmental organizations including Greenpeace, the Environmental Law Institute, the World Resources Institute, and the World Wildlife Fund. Influence Watch, citing the foundation’s grant database, reported that the Oak Foundation has positioned itself as a supporter of China’s Belt and Road Initiative.

APT also reports that the Oak Foundation has directed tens of millions of dollars to the Arabella network of advocacy groups, including $67 million to the New Venture Fund, $12 million to the Windward Fund, and $2.8 million to the Hopewell Fund. The Tides Foundation also received funding from Oak, according to the report.

The Copenhagen-based KR Foundation and the Swiss-based Laudes Foundation also provided funding to groups within the Arabella network. APT states that these two foundations have passed a combined $55.6 million to U.S. advocacy organizations. The KR Foundation was founded by descendants of Danish businessman Villum Kann Rasmussen, while the Laudes Foundation was established by the Brenninkmeijer family, a German-Dutch business dynasty.

Entities founded by Swiss billionaire Hansjörg Wyss ranked second on APT’s list. The Wyss Foundation and the Berger Action Fund have reportedly passed more than $673 million to U.S.-based advocacy groups.

APT alleges that groups funded by Wyss advance a progressive agenda, shape policy debates, and influence elections. The report states that Wyss-backed funding has supported organizations including the Fund for a Better Future, the League of Conservation Voters, the National Redistricting Action Fund, Planned Parenthood, and Indivisible.

In response, a spokesperson for the Wyss Foundation and the Berger Action Fund said the organizations “have always followed relevant rules, laws and disclosure requirements, and have prohibited their grants from being used to support or oppose political candidates or parties.”

The report also identifies two U.K.-based entities: the Children’s Investment Fund Foundation (CIFF) and the Quadrature Climate Foundation. According to APT, CIFF has directed approximately $638.2 million to U.S. advocacy groups, while the Quadrature Climate Foundation has passed roughly $532.5 million.

APT alleges that CIFF, backed by British billionaire Christopher Hohn, has engaged in advocacy related to climate change and social justice initiatives. The report also states that CIFF’s CEO is affiliated with organizations linked to China’s Belt and Road Initiative.

The Quadrature Climate Foundation, the philanthropic arm of London-based hedge fund Quadrature Capital, founded by Greg Skinner and Suneil Setiya, has directed funding to various environmental and policy organizations. APT reports that its largest recipient was the ClimateWorks Foundation, which received $147 million, including $25 million to support electric vehicle initiatives and $6 million for financial regulation efforts aimed at addressing climate risks.

“For years, foreign organizations and megadonors have quietly poured billions of dollars into the U.S. political sphere with little to no accountability,” APT stated in its report. “Foreign funding has infiltrated nearly every sector of the U.S. political sphere.”