Legal authorities in Iowa are considering an ethics complaint filed against Donald Trump’s acting attorney general, Matthew Whitaker, over his involvement in a company that defrauded customers.

The complaint accuses Whitaker of violating Iowa’s rules for attorneys through his work for World Patent Marketing. If upheld, it could ultimately result in Whitaker’s license to practice law being revoked.

It was filed by Gregory Sarno, an attorney in California opposed to Trump’s agenda. A disciplinary panel at the Iowa supreme court received the complaint late last month, according to records seen by the Guardian.

Sarno’s complaint said Whitaker served as an “enforcer” for World Patent Marketing, which was shut down in May by federal regulators who found it had cheated hopeful inventors out of millions of dollars. Whitaker was paid almost $10,000 to serve as a member of the firm’s advisory board.

“Matthew G Whitaker allegedly aided and abetted a fraudulent marketing scheme that cheated thousands of consumers,” Sarno’s eight-page complaint said.

Trump installed Whitaker as acting attorney general last month after firing Jeff Sessions. The president said last week he intended to nominate William Barr, an attorney general under former president George HW Bush, to be Sessions’s replacement.

Whitaker, a 49-year-old former federal prosecutor in southern Iowa, is licensed to practice law in the state and in Minnesota, where he worked as a private attorney from 1995 to 2001.

Iowa’s rules of professional conduct state that it is professional misconduct for an attorney to “engage in conduct involving dishonesty, fraud, deceit, or misrepresentation”. The rule, cited in Sarno’s complaint, applies even if the attorney is acting as a businessperson rather than giving legal representation.

Emails filed to court show that in August 2015, Whitaker sent a threatening email to a customer of World Patent Marketing who had complained about the company to the Better Business Bureau.

“I am assuming you understand that there could be serious civil and criminal consequences for you,” Whitaker wrote in the email. “Understand that we take threats like this quite seriously.”

Records released last month by the Federal Trade Commission (FTC) showed Whitaker received emails from World Patent Marketing customers about the company’s mistreatment of customers, typically forwarding them by email to the company’s founder, Scott Cooper.

Despite records and online video clips showing otherwise, Whitaker last year told the FTC inquiry into the company that he never emailed customers and “wouldn’t have personally ever said anything about the business”, according to an investigator’s notes.

Sarno’s complaint about Whitaker cites media reporting on his involvement in World Patent Marketing, including a Guardian article on military veterans who lost their life savings in the fraud.

Kerri Kupec, a justice department spokeswoman, did not respond to a request for comment. Previously she has said: “Acting Attorney General Matt Whitaker has said he was not aware of any fraudulent activity. Any stories suggesting otherwise are false.”

The FTC concluded that customers paid World Patent Marketing tens of thousands of dollars to patent and market their inventions based on bogus “success stories” and often did nothing.

“After stringing consumers along for months or even years, the defendants did not deliver what they promised, and many people ended up in debt or lost their life savings with nothing to show for it,” the FTC said.

The complaint also accuses Whitaker of violating rules on truthfulness in statements to others.

Under Iowa court rules, the complaint against Whitaker is confidential and will first be reviewed by the state supreme court’s attorney disciplinary board, which is made up of nine lawyers and three non-lawyers.

The board may dismiss the complaint, recommend a reprimand of Whitaker, or decide to prosecute the complaint at a private hearing of a grievance commission, which is made up of four lawyers and one non-lawyer. Whitaker would be entitled to defend himself. The commission may also dismiss the complaint, privately or publicly reprimand Whitaker, or recommend the suspension or revocation of Whitaker’s license.

If the complaint against Whitaker were to get that far, the Iowa supreme court would then consider the commission’s findings and issue a verdict on his punishment.