Thomas-Greenfield made the remark after lawmakers on the Senate Foreign Relations Committee asked her whether the large bill the US owes to the UN is obstructing her work.
"That is really the crux of the challenge that I face in New York every single day, as we are put in a position of having to compete with our adversaries on being able to influence the UN's actions, including staff who are capable in the United Nations," Thomas-Greenfield said.
The US envoy said she and her American collages are reminded publicly about the debt at the UN in what she called attempts "to shame."
"We don't feel shame that we have such a large debt, such large arrears in the United Nations. So we really do have to address that issue if we are going to be able to compete," the Ambassador said.
Thomas-Greenfield also warned the committee that every gap the US leaves open, including staffing or funding of the organization, will be filled by the Chinese.
The ambassador spoke during a hearing on the US response to the global food crisis. US Agency for International Development Administrator Samantha Power joined Thomas-Greenfield in testifying during the hearing.