The Youngs were the third-highest American donors last year in the Chronicle of Philanthropy's list of biggest philanthropists.
Their $423.4 million in donations last year, mainly to support their Laura and John Arnold Foundation, trailed only giving by Warren Buffett and Mark Zuckerberg and wife Priscilla Chan.
Leila Walsh, a spokeswoman for the Laura and John Arnold Foundation, who does not represent the Arnolds as individuals, said that public employees in cities and states across the U.S. are being "shortchanged by systems that allow politicians to promise one level of benefits without fully funding them."
"Workers deserve more than false promises," according to a statement by Walsh explaining the foundation's principles of pension reform. "LJAF believes that all public employees, regardless of tenure or when they were hired, ought to have a path to a secure retirement. We work with cities and states, Democrats and Republicans, to help them develop solutions that protect workers and taxpayers."