A senior adviser to US President Donald Trump, Kellyanne Conway, may have violated federal ethics rules by using her position to promote product lines of Trump's daughter, Ivanka, according to legal experts and congressional lawmakers.

The White House on Thursday “counseled” Conway, who is the Counselor to the President, in an unusual show of displeasure after she urged consumers to buy fashion products marketed by the president’s daughter.

Asked at a press briefing on Thursday if Conway had crossed an ethical line, White House press secretary Sean Spicer said, "She has been counseled on that subject, and that's it,” without elaborating further.

"Go buy Ivanka's stuff... I'm going to go get some myself today," Conway told Fox News in an interview on Thursday from the White House. "I'm going to give a free commercial here: Go buy it today, everybody; you can find it online.”

Conway’s comments also drew a sharp and unusual rebuke from a top Republican congressman, House of Representatives Oversight Committee Chairman Jason Chaffetz, who said that Conway’s comments were “absolutely wrong, wrong, wrong” and “clearly over the line.”

Federal ethics rules prohibit executive branch employees from using their positions to endorse products or promote an associate’s financial interests.

Legal experts described Conway’s remarks as a direct violation of Office of Government Ethics (OGE) rules.

Don W. Fox, a former OGE acting director and general counsel, said Conway’s statements were “jaw-dropping” and “a clear violation of rules prohibiting misuse of public office for anyone’s private gain.

On Wednesday, Trump rebuked the Nordstrom department store chain for dropping his daughter's products, drawing intense criticism for using a White House twitter platform to intervene in a commercial matter involving his family's business ties.

Nordstrom said it dropped the brand for its declining sales.

Trump has faced criticism from Democratic lawmakers and ethics experts who have warned that his political power could be misused to enrich him and his family.