United Nations Ambassador Nikki Haley's abrupt resignation on Tuesday came one day after an ethics group requested the State Department's inspector general investigate her acceptance of seven free flights aboard private jets.

Haley, the former governor of South Carolina, listed the flights on her 2017 financial disclosure and asserted that each qualified for an exception based on her relationships with the trio of businessmen who provided them.

But the group suggested that Haley did not provide enough information to assert that exception.

United Nations Ambassador Nikki Haley's abrupt resignation on Tuesday came one day after an ethics watchdog group requested the State Department's inspector general investigate her acceptance of seven free flights aboard private jets from a trio of South Carolina businessmen.

Haley, the former governor of South Carolina, listed the flights on her 2017 financial disclosure and asserted that each qualified for an exception based on her relationships with the businessmen.

But the group, Citizens for Responsibility and Ethics in Washington, said in its complaint that Haley's financial disclosure did not provide enough information to make the assertion that the flights between New York, Washington, DC, and three South Carolina cities qualified for the exemption.

Those flights were most likely worth tens of thousands of dollars, CREW suggested.

"Whether the exception applies depends partly on whether the three businessmen were the only sources of the gifts; if business entities were sources of the gifts, the exception was inapplicable," CREW said. "Federal ethics regulations prohibit employees from soliciting or accepting gifts given because of the employee's official position."

The three businessmen who provided the flights to Haley and her husband were Jimmy Gibbs, Smyth McKissick, and Mikee Johnson. Gibbs is the CEO of Gibbs International, and McKissick and Johnson are CEOs of private companies in South Carolina.

Johnson is chair of The Original Six Foundation, which Haley founded in 2011. McKissick is chairman of Clemson University's board of trustees. Haley is a graduate of the university and her daughter is currently enrolled there as a student.

"By accepting gifts of luxury private flights, Ambassador Haley seems to be falling in line with other Trump administration officials who are reaping personal benefits from their public positions," CREW's executive director, Noah Bookbinder, said in a Monday statement.

Tom Price resigned as the secretary of health and human services last year amid a controversy involving his air travel. Other top Trump administration officials, including Treasury Secretary Steven Mnuchin and former Environmental Protection Agency Administrator Scott Pruitt, have come under fire for their air-travel practices.

Walter Shaub, the former director of the Office of Government Ethics, noted on Twitter on Tuesday that Haley's resignation came after CREW filed its complaint.

Haley's resignation caught Washington, DC, and the diplomatic community by surprise. She announced her departure less than a month after the United Nations General Assembly in New York.

Haley was one of the foreign-policy and Washington establishments' favorite Trump administration leaders. Some had even speculated that she would soon run for president.

In announcing her resignation alongside President Donald Trump in the Oval Office on Tuesday, Haley knocked down any speculation that she would run for president in 2020, saying she would campaign for Trump.

"It has been an honor of a lifetime," Haley said of serving as UN ambassador.

In the meeting, Trump told reporters that Haley told him about six months ago that she would want to depart from the job after serving for two years. He added that she would stay on through the end of the year.

"She's done a fantastic job, and we've done a fantastic job together," Trump said.