Last week, US department store chain Nordstrom dropped Ivanaka Trump’s clothing line following declining sales.

And of course, instead of focusing on his actual job, Donald Trump tweeted angrily about it.

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

When Trump has explicitly criticised companies in tweets before, it has affected their stock market value – he wiped $1 billion of Boeing’s stock when he said that costs for the company’s new Air Force One were out of control, and Toyota also experienced a similar loss when Trump mentioned them.

But at least both those were issues that the US President should be involved in – Air Force One, and American jobs. Tweeting about his daughter’s business is very different, and again highlights the conflict of interest concerns many have about Trump’s presidency.

Now ethicists are even suggesting that Nordstrom may have grounds to sue Trump over his tweet.

Norm Eisen, a former White House ethics lawyer and current chair of Citizens for Responsibility and Ethics in Washington (CREW), even offered up his help:

Outrageous. Nordstrom, others injured should consider suing, incl. under CA Unfair Comp Law, forbidding "any unfair biz act." I will help!

Jordan Libowitz, a spokesman for CREW, added:

Knowing that he's doing it just for his family's business interest is disturbing. The real question to ask is how does it benefit [Jared] Kushner?

Jared Kushner is of course Ivanka Trump’s husband, and a senior advisor to the President.