A campaign led by a U.N. whistle-blower that successfully changed U.S. law could cost the United Nations hundreds of millions of dollars if it doesn’t adhere to “best practices” to protect any U.N. employee who reports wrongdoing.

The appropriations bill signed by President Barack Obama on Jan. 17 contains a provision to automatically withhold 15 percent of U.S. funding for the United Nations or any of its agencies unless — or until — Secretary of State John Kerry certifies to Congress that its conduct toward whistle-blowers meets five “best practices.”

U.N. deputy spokesman Farhan Haq said Friday that the U.N. took note of the U.S. decision “while we continue to apply our whistle-blower protection policies throughout the U.N. system.”

James Wasserstrom, an American who accused senior colleagues of retaliating after he alleged corruption in the U.N. peacekeeping mission in Kosovo, said in an interview that the new law is “a major step in the right direction to put pressure on the United Nations and all of its agencies to clean up their acts when it comes to internal corruption.”

“This is not a U.S.-U.N. issue,” stressed Wasserstrom, who led the campaign to change the U.S. law. “This is an issue that affects all major donors. They should all be demanding immediate reforms of the U.N. in fighting fraud, waste and abuse.”

Wasserstrom, who was the lead anti-corruption officer at the Kosovo Mission in 2007, was awarded $65,000 after the U.N. Dispute Tribunal ruled that he was subjected to “wholly unacceptable treatment” and “appalling” acts in violation of the rule of law and human rights. The United Nations is appealing the ruling and the award, and Wasserstrom’s attorneys are appealing the amount of the award, saying it is insufficient.

The “best practices” requirement had been in place since 2012, but until now if the secretary of state remained silent, there was no withholding of U.S. funds to the United Nations.

The U.S. pays 22 percent of the U.N.’s regular budget, which for 2014-2015 totals $5.53 billion. It also pays hundreds of millions of dollars for the separate budgets to cover U.N. peacekeeping operations and the work of U.N. agencies that deal with children, refugees, food, agriculture and other global issues.

Wasserstrom said that with the help of the Government Accountability Project, a Washington-based whistle-blower protection organization, he went to Capitol Hill and talked to congressional staffers in both chambers, from both sides of the aisle, “and they were receptive.”

Dylan Blaylock, a spokesman for the Government Accountability Project, said, “Problems involving corruption at the United Nations remain widespread, and this new requirement will help protect whistle-blowers like James Wasserstrom who are simply trying to expose wrongdoing so it can be corrected.”

According to the bill, the U.N. must protect whistle-blowers against retaliation, permit access to independent tribunals including external arbitration, and ensure financial compensation and restoration of reputation for proven retaliation. It must also apply best practices on the amount of evidence that it takes to prove retaliation and on how long a U.N. employee has to challenge retaliation.

The U.N. Secretariat’s policy on protection against retaliation for whistle-blowers went into effect in January 2006 and provides a process for reviewing complaints, investigating those where “a prima facie case of retaliation has been determined,” making a final determination and identifying remedies.

“The United Nations remains committed to ensuring that its policy reflects best practices,” the U.N.’s policy statement says.

It concludes that an independent examination of the U.N. policy and its implementation by an international judge is currently being reviewed by the U.N. “with a view to identifying ways to further strengthen the U.N.’s commitment to protect whistle-blowers.”