WASHINGTON (WASHINGTON POST) - US President Donald Trump has criticised Nordstrom for dropping his daughter Ivanka's brand from the department-store chain, drawing a new company into his ongoing skirmishes with corporate America.

"My daughter Ivanka has been treated so unfairly," Trump said on his personal Twitter account on Wednesday (Feb 8).

"She is a great person - always pushing me to do the right thing! Terrible!"

The tweet was later - controversially - retweeted by the President's official @POTUS account.

Nordstrom said last week that it would stop selling Ivanka Trump's brand this season, citing poor sales.

The retailer had come under fire from the Grab Your Wallet campaign, a critic of the administration, which is asking shoppers to boycott retailers that carry Ivanka Trump or Donald Trump goods.

Trump's tweet renewed questions about whether he's using the presidential pulpit to sway business interests for himself or his family.

In addition to starting a lifestyle brand, Ivanka Trump has worked for the Trump Organisation, and husband Jared Kushner serves as a presidential adviser.

Ivanka Trump said last month that she was handing day-to-day operations of her brand to lieutenant Abigail Klem.

"It's never great to have these questions about dual allegiance," said Jordan Libowitz, communications director for Citizens for Responsibility and Ethics in Washington, a nonpartisan watchdog group.

"But certainly we've never seen before a president using the power of the presidency to pressure businesses for the obvious benefit of his family."

Sean Spicer, Trump's press secretary, defended Trump's tweet to reporters during a briefing on Wednesday, saying "He has every right to stand up for his family and applaud their business activities, their success."

Spicer also said, "This is a direct attack on his policies and her name."

Ivanka Trump's brand didn't have an immediate comment.

Shares of Nordstrom dipped after Wednesday's tweet was posted, though they quickly recovered. As of 11.43am in New York, the stock was up 0.1 per cent at US$42.84.

Once again, a company was engulfed in a political controversy with a single tweet from the President. Trump's personal account has 24 million followers, and he has frequently used it to browbeat companies - often without warning.

Lockheed Martin was a target last year, when then President-elect Trump said the costs of the F-35 fighter jet were out of control. The comment sent the stock down 2.5 per cent and erased almost US$2 billion in market value.

He's also used his account to praise companies, such as LL Bean. In January, he urged people to buy products from the catalogue retailer after the founder's granddaughter sparked controversy by donating to a political action committee that supported his campaign.

Since becoming president on Jan 20, Trump has also used the official presidential account @POTUS.

The Nordstrom tweet was not sent from that account initially, but it was retweeted from it.

Nordstrom had been an early supporter of Ivanka Trump's brand after it launched in 2011. It was one of the first retailers to offer wares, which include shoes, apparel and accessories.

But recently her products began to disappear from its inventory, raising questions about the relationship.

That's when the chain confirmed that it decided not to reorder the brand's merchandise.

"Based on the brand's performance, we've decided not to buy it for this season," the company said last week.