US President Donald Trump has hit out at Nordstrom for dropping his daughter, Ivanka's clothing line.

The company ceased selling Ivanka's line because sales fell, amid a boycott by some people of stores selling brands associated with the president as part of the #grabyourwallet campaign.

Trump tweeted: "My daughter Ivanka has been treated so unfairly by ‪@Nordstrom. She is a great person -- always pushing me to do the right thing! Terrible!"

Ivanka Trump has not made any similar statements on Twitter, and Nordstrom has said it frequently makes decisions not to re-buy brands, in decisions based on how well those brands sell, Reuters reported.

As well as Nordstrom, retailer Neiman Marcus Group also reportedly said it had stopped selling Ivanka Trump's line, which includes clothing and accessories.

The president's daughter has moved with her family to Washington DC and has taken a step back from her role with The Trump Organization to help her father in his new capacity – although she does not have an official title at the White House.

Trump's tweet taking a shot at Nordstrom is the first time the president has hit out at a company associated with his family since he was sworn in, although he has hit out at other entities and individuals since becoming president.

Trump's use of twitter has prompted concern from many politicians, who questioned whether he would continue his prolific social media use after becoming president – which he has done so far.