Mr Trump tweeted that “Ivanka has been treated so unfairly” by clothing retailer Nordstrom.
A Democratic senator called the post “inappropriate” and an ex-White House ethics tsar dubbed it “outrageous”.
Earlier this month Nordstrom became the fifth retailer to drop the Ivanka Trump clothing line, citing lack of sales.
The move comes amid a boycott of all Trump products, which activists have dubbed #GrabYourWallet, in reference to a 2005 comment Mr Trump made about women’s bodies.
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A spokesman for Pennsylvania Senator Bob Casey said the senator “feels it is unethical and inappropriate for the president to lash out at a private company for refusing to enrich his family”.
Norm Eisen, who served as ethics tsar under President Barack Obama, called the move “outrageous” and advised Nordstrom to sue Mr Trump under the California Unfair Competition Law.
The White House has played down the row.
Press spokesman Sean Spicer said that Nordstrom’s decision was political, and the president was simply reacting to “an attack” on his daughter.
“This is a direct attack on his policies and her name and so there’s clearly an attempt for [the president] to stand up for her being maligned because they have a problem with his policies,” Mr Spicer said during the daily press briefing.
Nordstrom has yet to respond to the recent tweet, but have said previously that the decision to drop the Ivanka Trump line was “based on the brand’s performance.”
The tweet, which was sent by Mr Trump’s @realDonaldTrump account was then retweeted by the official @POTUS account.
Shares in the retailer fell 0.7%, before rallying slightly by midday.
Earlier this week, First Lady Melania Trump came under fire after she re-filed a lawsuit against the Daily Mail over false allegations that she once worked as an escort.
Her lawyers accused the news website of trying to deny her a “once-in-a-lifetime opportunity” to profit from her position as “one of the most photographed women in the world”.
Critics accused the First Lady of improperly seeking to profit financially from her White House position.
Mrs Trump is seeking damages of $150m (£120m).