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Kellyanne Conway, counselor to President Donald Trump, acted "inadvertently" when she told Americans to "go buy Ivanka's stuff" and has promised never to do it again, the White House ethics office said in a letter made public Wednesday.

The U.S. Office of Government Ethics, a separate and independent executive branch agency, warned the White House that it had "strong reason" to believe that Conway violated ethics rules when she appeared Feb. 9 on Fox News' "Fox & Friends" and made an extensive pitch for Ivanka Trump's clothing line.

"Go buy Ivanka's stuff," Conway said. "I own some of it. I fully — I'm going to just, going to give a free commercial here. Go buy it today, everybody. You can find it online," she added.

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Jason Chaffetz, R-Utah, and Elijah Cummings of Maryland — chairman and ranking Democrat, respectively, of the House Committee on Oversight and Government Reform — swiftly asked the White House Office of Compliance and Ethics to respond to the comments.

"That was wrong, wrong, wrong," Chaffetz told NBC News last month. "It is wholly unacceptable — no if, ands or buts about it."

In a letter (PDF) dated Monday and provided Wednesday night by Democrats on the committee, Stefan Passantino, head of the White House's ethics office, wrote that "we concluded that Ms. Conway acted inadvertently and is highly unlikely to do so again."

Passantino said that Conway "made the statement in question in a light, off-hand manner" and that she "did so without nefarious motive or intent to benefit personally." The U.S. Office of Government Ethics has yet to rule on the matter.

Specifically, Passantino said, Conway was defending Ivanka Trump against a backlash her father created when he strongly criticized the retail chain Nordstrom for having dropped her clothing line from its stores.

My daughter Ivanka has been treated so unfairly by @Nordstrom. She is a great person -- always pushing me to do the right thing! Terrible! — Donald J. Trump (@realDonaldTrump) February 8, 2017

Conway wasn't seeking to profit from the endorsement, Passantino said; instead, she was "attempting to stand up for a person she believed had been unfairly treated."

"This administration is committed to complying with the ethical obligations set forth in the Standards of Conduct," he wrote, adding: "Ms. Conway has acknowledged her understanding of the standards and has reiterated her commitment to abiding by them in the future."

Cummings said Wednesday that it was a "bad sign" that "the president chose not to discipline Ms. Conway for blatantly violating the law."

The White House told NBC News: "The letter speaks for itself."

NBC News reported last month that the Office of Government Ethics website crashed on the day Conway delivered her plug because of what the agency called "an extraordinary volume of contacts from citizens about recent events."