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.