In 2017, Frelinghuysen wrote a campaign fundraising letter to a board member of a local bank. While Frelinghuysen did not name NJ 11th for Change, a progressive lobbying group, he included a handwritten postscript warning "One of the ringleaders works in your bank!", with an attached news article about one of NJ 11th for Change's members. The individual subsequently resigned from her position as assistant general counsel and senior vice president at that bank, citing pressure over her political involvement as one of the reasons.