"We are working with Capitol Hill police to fully understand and appreciate the incident," principal assistant U.S. Attorney Channing Phillips told The Associated Press in a telephone interview.
Citing a continuing investigation, Phillips would not say whether the referral included a recommended charge against the six-term Democrat or when a warrant for her arrest might be issued.
In a statement, Capitol Police said it "has referred its investigative findings to the U.S. attorney." The department must obtain approval from U.S. Attorney Kenneth L. Wainstein before it can ask a judge to issue an arrest warrant on assault or other charges.
McKinney spokesman Coz Carson acknowledged the investigation.
"We're aware that the wheels are turning in Washington," Carson said. "We have no control over what they decide to do. We will make the appropriate statement and take the appropriate action once we know where they're going."
For her part, McKinney said she expects to represent her constituents in the suburbs of Atlanta, Georgia, for many years.
"Rest assured, I am doing the work they sent me to Washington to do. Nothing is going to keep me away from my responsibilities," McKinney told a crowd of supporters in Atlanta on Monday.