Winfrey's lawyers say the talk show host has the rights to the "aha moment" slogan and they do not want to mislead fans into thinking she is associated with the company.
Mutual of Omaha answered the letter with a lawsuit, claiming even if Winfrey had trademark rights, she abandoned them by failing to police the phrase when other businesses used it in the past.
Winfrey's company, Harpo, said it hoped to reach an amicable resolution on the issue.
