New Zealand businessman Christopher Liddell is at the centre of an ethics controversy at the White House, Politico reports.

Matamata-born Liddell, a former Microsoft and General Motors executive, was appointed by US President Donald Trump as an assistant.

But Citizens for Responsibility and Ethics in Washington is accusing Liddell of potentially violating criminal conflict of interest laws.

Politico reports that the watchdog says Liddell played a role in meetings with major companies "in which he also appeared to have held millions of dollars in stock".

The group filed its complaint today saying Liddell might have broken the law over three days in January and early February. He took part in policy meetings between Trump and leaders from up to 18 companies that he also had a financial interest in.

They included the Ford Motor Company, Johnson & Johnson and General Motors.

Politico reports that the group cited Liddell's certificate of divestiture forms, issued by the Office of Government Ethics last month, which listed the companies he and his wife held stocks in through a trust.

The watchdog said that the White House meetings took place on January 23 and 24, and February 3, before his certificate came out. The meetings covered tax, regulatory, infrastructure and investment policies.

It said that "strongly indicates Mr Liddell still held stock in the companies at that point and had not divested his financial interests in these assets prior to his participation in the meetings".

The group's letter is to White House Counsel Don McGahn. Citizens for Responsibility and Ethics in Washington has asked him to determine whether a Justice Department probe was required.

The White House did not immediately respond to a Politico request for comment on the complaint.