"The Office of Special Counsel issued Haley a warning letter noting that any future engagement in prohibited political activity will be considered 'a willful and knowing violation of the law, which could result in further action,'" according to a press release from the Citizens for Responsibility and Ethics (CREW), which filed the original complaint.
The Hatch Act
prohibits employees in the executive branch, except the President, vice president and some other high-level officials, from engaging in political activity.
A spokesperson for the OSC told CNN that they do not comment on the status of such investigations.
Haley did not immediately respond to CNN's request for comment.
CREW's initial complaint stemmed from Haley's retweet of a post by Trump that said: "Ralph Norman, who is running for Congress in SC's 5th District, will be a fantastic help to me in cutting taxes."
"This is already the third time this year that a senior Trump official has been reprimanded for misusing their official position following a CREW complaint," CREW Executive Director Noah Bookbinder said in a written statement. "Ambassador Haley should have known better."
Senior White House aide Dan Scavino was reprimanded in April by the OSC
for violating the Hatch Act in a tweet calling for the defeat of GOP Rep. Justin Amash in a primary, according to a letter posted by CREW.
Scavino's tweet came on the heels of Trump's taking to Twitter in April to call out the conservative House Freedom Caucus, which Amash is a member of, for not supporting his plan to repeal and replace Obamacare.
Counselor to the President Kellyanne Conway was also rebuked in February for violating federal ethics regulations by using her official position to promote Ivanka Trump products, according to the group.
"One is unfortunate, two is a coincidence, but three in less than a year is a pattern," Bookbinder said in a statement on Tuesday. "This all stems from the President's permissive attitude toward ethics; the tone is set at the top."