The White House should consider disciplinary action against presidential adviser Kellyanne Conway for appearing to violate government ethics rules by publicly endorsing Ivanka Trump products, the Office of Government Ethics wrote in a letter made public on Tuesday.

The letter, dated Monday and addressed to a White House ethics official, asked President Donald Trump's administration to investigate the incident and gave it two weeks to provide its findings and detail any disciplinary steps taken.

Conway, Trump's presidential campaign manager and now a senior counsellor, said on Fox News last week that Americans should "go buy Ivanka's stuff." She spoke after retailer Nordstrom announced it was dropping the branded line of Ivanka Trump, the president's older daughter.

Federal ethics rules prohibit executive branch employees from using their positions to endorse products.

"There is strong reason to believe that Ms. Conway has violated the Standards of Conduct and that disciplinary action is warranted," Office of Government Ethics Director Walter Shaub wrote in the letter.

Stefan Passantino, the White House ethics official named in the letter, declined to comment. A White House spokesman did not reply to a request for comment.

Open gallery view White House adviser Kellyanne Conway tweets 'I love you' at white nationalist Twitter account. February 14, 2017. Credit: Twitter, screen grab

The ethics office has little enforcement power. It can formally recommend disciplinary action if the White House does not act, Shaub said in a separate letter to two U.S. lawmakers who sought a review of Conway's remarks.

That recommendation would not be binding, and the process would take until late April or early May, Shaub said. If the ethics office does formally recommend discipline, it would be up to the White House to decide any steps against Conway.

Trump himself earlier attacked Nordstrom for dropping his daughter's brand.

"My daughter Ivanka has been treated so unfairly by @Nordstrom," he tweeted.

The ethics rules that bar endorsements do not apply to the president, though critics said his comments were inappropriate.

The same day the ethics office suggested disciplinary action against Conway, she tweeted a Valentine’s Day message at a white nationalist Twitter account "that has posted anti-Semitic and racist messages," according to the media watchdog Media Matters for America.

The Twitter account @TrumpTrainNoBrk tweeted at Conway on February 14: “Your strength & resiliency in face of vile hatred, bigotry, & sexism of the unhinged Left is a daily inspiration! Love you!” Conway responded to the tweet with a message saying, "Love you back."

Conway, later deleted the tweet and implied in an interview to Buzzfeed that she was not responsible for the tweet. " I do not know who had access to my account. ... Let me see who sent this.” She added, “I denounce whoever it is. It will be immediately deleted. Everybody makes mistakes.”

"The account’s white nationalist orientation is clear from just a cursory glance," wrote Media Matters, citing the cartoon pepe frog and "#WhiteIdentity" in the accounts biographical information.