Ajit Pai, a Republican member of the Federal Communications Commission, first suggested defunding the ITU last week.
"We should also make it clear that we will not sit passively as the ITU attempts to expand its purview even further. If the organization decides to become an international regulatory authority for the Internet, we will have to ask ourselves whether the United States should remain one of its two top funders," Pai said at a forum of the LGBT Technology Partnership.
Last year, 89 countries signed a treaty at an ITU conference giving the international body more control over the Internet. Supporters of the treaty argue it will help governments fight spam, bolster cybersecurity and expand Internet access. But the United States and other opponents warn it could lead to censorship and stifle Internet growth.
The ITU is scheduled to hold another conference next year in South Korea. The agency, which is part of the United Nations, also coordinates agreements on wireless spectrum, technical standards and other communications issues.