In early 2015, an anonymous comment accusing a Florida company of being a scam was posted on a consumer website called RipoffReport.com.

Around that time, the publication’s phone rang. The caller said he was Matthew Whitaker—now the acting attorney general—and he was angry, said Ed Magedson, owner of Ripoff Report. Using profanity, Mr. Whitaker demanded the removal of all negative reports about the company, World Patent Marketing Inc., Mr. Magedson said.

“He threatened me using a lot of foul language,” said Mr. Magedson, who added he had reviewed notes he made at the time. “He threatened to ruin my business if I didn’t remove the reports. He [said he] would have the government shut me down under some homeland security law.”

Ripoff Report itself has been subject to criticism, with detractors saying it has profited from the negative reports posted on its website.

Since President Trump appointed Mr. Whitaker last week, the acting attorney general has faced questions about the extent of his involvement with World Patent Marketing, where he was a paid advisory-board member until at least 2016. The company was shut down last year by the Federal Trade Commission after it accused the firm of scamming $26 million.